To Build Open and Evolutive Applications an Approach based on MDA and Generative Programmin

To Build Open and Evolutive Applications:an Approach based on MDA and

Generative Programming?

Carine Courbis

University College London

Computer science department Adastral Park-Martlesham IP53RE-UK Carine.Courbis@https://www.wendangku.net/doc/17390542.html,

Philippe Lahire

Laboratoire I3S(UNSA/CNRS)

2000route des lucioles BP121

F-06903Sophia-Antipolis CEDEX,France https://www.wendangku.net/doc/17390542.html,hire@unice.fr

Didier Parigot

INRIA Sophia-Antipolis

2004,route des Lucioles-BP93

F-06902Sophia-Antipolis CEDEX,France Didier.Parigot@sophia.inria.fr

Abstract

With the emergence of the Internet and proliferation of new component and distributive technologies,the design and implementation of complex applications has to take into account standards,code distribution,deployment of compo-nents and reuse of business know-hows.To cope with these changes,applications need to be more open,adaptable and evolutive.

To accommodate to these new challenges,this paper presents a new development approach based on transfor-mations of different business models,each of them related to one possible concern of the application.This approach is MDA(Model-driven Architecture)compliant and relies on Generative Programming.It contributes to the research works on Domain Driven Development(DDD).The main expected results are i)to get softwares of better quality thanks to business models and technology separation,ii)to have a more straightforward code,iii)to allow the rapid development and insertion of new facets and iv)to facilitate the portability of applications towards new technologies or platforms.

Finaly,in order to illustrate our approach,a generative programming system,called S MART T OOLS,is presented. It may be compared to a software factory dedicated to ap-plications which rely on one data model.

?This project is supported in part by the W3C consortiun with the IST-2000-28767QUESTION-HOW Project.We would also like to thank P AS-CAL D EGENNE and A LEXANDRE F AU for their software development ef-forts in S MART T OOLS.1.Introduction

During this last decade,there were many changes in computer science that have an in?uence upon the way an application must be developed.To cope with these changes, applications need to be more open,adaptable and evolutive. Before going any further,we explain why these new con-straints in software development have emerged.

?The?rst reason is that the emergence of the Internet requires applications to be no more PC-enclosed but rather distributed.Thus,from now,data communica-tion between applications and users must be taken into account during the whole application life-cycle.One important point is to choose a well-adapted data ex-change format.

?The second reason of these changes is the prolifera-tion of new component technologies.It makes dif?cult to choose the one which is the more adapted and the most evolution-prone according to the context of use.

For instance it will be necessary to decide whether it is better to take CCM(CORBA Component Model),EJB (Entreprise Java Bean),or COM(Component Object Model),etc.

?The third reason is the democratization(widespread) of computer https://www.wendangku.net/doc/17390542.html,ers may have now different knowledges,different needs,a wide range of visualiza-tion devices,and speci?c activity domains.This aspect should be considered when designing and developing applications.

?The last reason is business related.Indeed,to be com-petitive a company must quickly and cheaply adapt its software to new user needs and technologies.

In software engineering,object-oriented programming is not always suf?cient to handle clear designs and reusable developments of software.For example,concerns can be cross-cut between classes and there can be a mix between functional and non-functional code in a single class mak-ing the code dif?cult to maintain and debug.This situation explains the need to provide new programming paradigms such as AOP(Aspect-Oriented Programming)[19],SOP (Subject-Oriented Programming)[14],IP(Intentional Pro-gramming)[33],or component programming[35].

At the speci?cation level,a strong and continuous evo-lution is undergoing towards standards of the W3C(World Wide Web Consortium)for documents or of the OMG(Ob-ject Management Group)for design methodologies such as UML(Uni?ed Modeling Language)or the MDA(Model-Driven Architecture)approach[13,37].

It seems that having only one model like in UML to tackle all the possible concerns of applications does not al-ways provide the most comprehensive approach to specify them.Moreover,the semantics associated to each UML en-tities is not very well speci?ed and is sometimes ambigu-ous.This is a strong drawback if the model need to be exe-cutable.

In order to better address these new challenges,we pro-pose an approach which relies on both MDA and Generative Programming[9].It promotes following key-ideas:?when the software is being designed and implemented different concerns are addressed by the programmer.

These concerns are better handled if a dedicated model1exists for each of them.Among the possible concerns there are the design of the application data-model,the management of persistence,the speci?ca-tion of security,the de?nition of GUI(Graphical User Interface),the handling of software components,etc.?if the model(dedicated to one of the concerns)is inde-pendent from the software platform on which the ap-plication will run,then it is possible to capitalize the know-how of the application independently from the context of use.Then the representation of the domain-speci?c knowledge is much more reusable.?Generative Programming paradigm is a powerful ap-proach which allows to compose all the different parts handled by those speci?c models in order to build the application according to the context of use(e.g.tech-nologies related to software platforms).

1By construction it will?t exactly to the needs of the concern.

Our approach relies on the concept of software factory [9].First we give an overview of our approach,then we provide more details about some of the models that may be used during the design and development process of an ap-plication.In particular we provide details about the imple-mentation of these models in the framework of the S MART-T OOLS software[31].Finally we compare our approach with the state of the art.

2.Overview of the approach

We propose an approach that we think more adapted to the design and implementation of applications which rely on one data-model.It conforms to ideas developped in re-search works dealing with Domain Driven Development.It is mainly based on the ability to de?ne business models and then to perform transformations on those models in order to generate either re?nements of those models or platform-speci?c models.

We promote the idea that the use of this approach al-lows to get open,adaptable,and evolutive software.More precisely,thanks to generative programming,new program-ming paradigms and technologies can be easily integrated from the models into the target implementation program-ming language,at any time.

In?gure1we aim to show the impact of our approach on the development of an application.Let us assume that to de?ne an application we need to:

?de?ne the data model associated with the application.

It could be an information system,a programming lan-guage,an Object-Oriented method but also any other business model.

?specify the semantics of the model,that is to say the set of rules that manage all instances of the model and the properties that may be implicitly suggested by some of the model entities.

?design the architecture of an application as a set of software components that interact one with the others.

Then it is necessary to be able to describe those com-ponents with their interactions.

?implement some orthogonal services such as persis-tence management,data integrity,distribution of ob-jects over the network,GUI,etc.

According to those needs and to the key-ideas mentioned in section1),we propose in?gure1to address four models. Each of them is dedicated to the speci?cations related to one concern:the data model,the semantics,the set of compo-nents and an additional(orhtogonal)service.Of course an application may rely on other(s)service(s).Depending on

Figure1.Our approach applied to the devel-

opment of an application

the application needs it will be a replacement or an addition of service(s).

Thanks to the use of domain-speci?c and platform inde-pendent models(PIM),the business model is speci?ed by parts which are independents from the platform on which it will be applied:persistence and security could be handled by any database management systems(DBMS),the model of components used may be EJB,CCM from OMG or any other(like the Web services from W3C),the language used to implement the model or its semantics may not be known at design time.

The generators associated to those models will then han-dle the generation of the application,providing the glue which is necessary to make it working on a speci?c plat-form,according to the context of use.If the platform changes or if the technology of the platform evolves,it is not necessary to update the models which represent the domain-speci?c know-how,but the generators only.In the next sec-tions we intend to give more details on the four models that we consider as mandatory in the development process of an application:

?the data model.It describes the application structure and should have an application-independent format in order to cut from the technology-speci?c details;?the semantic model.It integrates some facilities in order to structure and to modularize the code.This should help to maintain it and to facilitate its reuse;?the component model.It is as close as possible from

the application needs.In particular it allows to specify the provided and required services.

?the GUI model.It de?ne several views of the data model such as a structured editor in order to create and update more easily instances of this model;they must be device-independent.

In order to convince the reader with the interest of sep-arating the concerns through different models,we propose a more detailed description of those models and additional explanations about the handling of those models in S MART-T OOLS2.The experience of S MART T OOLS aims to i)give a more precise description of the approach and ii)show how the approach favours the possible adaptations of an appli-cation according to the future evolutions of the software platform.In order to summarize,let us come back on the key-aspects of our approach.

First,it follows the MDA approach(see?gure2).In par-ticular it uses source code generation as one transformation mechanism in order to produce one or many Platform Spe-ci?c Models(PSM),from the Platform Independent Model (PIM)such as those mentioned above.We claim also that the development process of open and adaptable applications should rely on several PIMs.

Figure2.Generative Programming and MDA

approach

Secondly our approach deals with the speci?cation of a generative programming system which had been compared by Krzysztof Czarnecki and Ulrich W.Eisenecker to a fac-tory of a particular domain[9].It could be applied to any application which has a underlying data model.

2S MART T OOLS is a research prototype whose aim is to validate our approach for different domains in an homogeneous way.

3.Data Models

In research works on programming languages,there are many formalisms to declare data structures(types).These formalisms are bound to either an underlying theory,asso-ciated systems(e.g.algebraic types for rewrite systems), or programming languages(e.g.ML language[22]).The most famous theory is certainly the notion of abstract syn-tax(very often mapped to a tree structure description)that contains the common concepts of those theories.Among them there is the concept of meta-language that may be rep-resented by a BNF-Backus Naur Form.

For some years,the standardization efforts of both OMG and W3C play major roles in the data and model integra-tion problematic.These standard formalisms continuously evolve in order to better address the new needs of applica-tions.For instance,to improve document data validation, the document meta-language(DTD-Document Type Def-inition)has been replaced by more complex and rich data type formalisms such as XML Schema or RDFS(Resource Description Framework Schema).Another example deals with object-oriented modeling:the UML approach has evolved toward a domain-speci?c model de?nition based on the MOF(Meta-Object Facility)meta-formalism[12].The databases have also evolved from relational databases to-ward object databases[5]and then toward XML databases [3].

Implementation:the experience of S MART T OOLS. Instead of using the formalisms mentioned above,we have preferred to de?ne our own abstract data meta-model which is close to our needs and independent from any for-malism.This meta-model aims to de?ne the business mod-els associated with the application.It has a leading role ac-cording to those various formalisms(DTD,XML Schema or MOF).For instance,we have de?ned translators(in both ways)between our meta-model and the DTD or the XML Schema meta-models.They make possible to import mod-els in S MART T OOLS as either a DTD,an XML Schema, or a document compliant to our meta-model.For example, this meta-model may be used to de?ne the abstract syntax of existing programming languages as well as domain-speci?c languages;it is the cornerstone for all the generated tools and components.The goals of a such meta-model are the followings:

?to cut off from existing formalisms;

?to open S MART T OOLS towards applications based on XML or UML standards;

?to bene?t from the development efforts(tools)made around these standards.

From this data model,S MART T OOLS can generate,as shown by?gure2,following capabilities:

?an API.It helps to the manipulation of abstract syntax trees(for instance,in order to write semantic analy-ses);

?an equivalent DTD or XML Schema.It provides some facilities to the designers for exporting models;

?an editor guided by the syntax.It is a basic GUI that may be generated automatically in order to facilitate the handling of instances of the model.

In order to avoid the design and the implementation of another propriatory tree manipulation API,we have chosen the DOM(Document Object Model)API standard as tree kernel.In this way,the code which is speci?c to S MART-T OOLS for manipulating trees is minimal thus easy to main-tain.Moreover our tree implementation bene?ts from any new service and bug?xing when this standard and its dif-ferent implementations evolve.Thus our tree implemen-tation is open,evolutive and can bene?t from any DOM-compliant tool or service.For example,all the trees manip-ulated in S MART T OOLS can be serialized in XML(see?g-ure3),transformed with XSLT(Extensible Stylesheet Lan-guage Transformation),or addressed with XPath for free as these services are provided by the DOM API.

DTD

or

model

generate

Document

is

conform

is

instance

of

Figure3.Bridge between languages and doc-

uments

One of the drawbacks about using the DOM standard is that it does not ful?ll all our needs:the manipulated trees are not strictly-typed(a DOM tree has only homoge-neous nodes).The main consequence is that it is dif?cult to semantically analyze them with a visitor-pattern approach (see section4).The handling of strictly-typed trees may be achieved thanks to the generation of a language-speci?c API(Java classes)above the DOM API(type names of the nodes and the name of accessors are provided by the model).

4.Semantic Models

Let us coming back on the fact that one of our main goal is that the semantics which is associated to the model should

allow the model to be executable.Starting from this re-quirement we propose a pragmatic approach which rely on approaches applied to the speci?cation of semantics within programming language and design methods.An interesting side effect of this choice is to reduce the gap between the design of an application and its implementation.

On the?rst hand,existing models like UML[28]or MOF[12]provide features for specifying the entities of a model as well as constraints on those entities;moreover works on action semantics[34]propose a graphical lan-guage for de?ning the body of methods but it seems that much remain to be done to make the model executable.

On the second hand,one of the approach which is ap-plied to the implementation of the semantics of program-ming language within compilers is based on the description of pieces of code.They are written in the language which is used for the implementation of the compiler.

According to this background our approach wants to take the bene?ts from programming languages and OO design methods.First it includes a way to de?ne the semantics of entities of the data model through a set of routines speci?ed with one programming language which acts on the model entities(they are named:actions).The expressiveness of such approach is straightforward but it is quite crude.A more declarative and structured approach would help the designer of the model to describe the semantics.

Later in this section we propose an overview of our pro-posal for the de?nition of the semantics related to the data model.It takes into account some capabilities allowing to:?split and compose the description of the semantics ac-

cording to the different concerns related to the model and its instances,

?factorize the common semantics of the model entities by the use of meta-information and meta-assertion[8],?specify better the different actions associated to model entities

A clear distinction should be made between people who describes the model3,and people who uses it and create in-stances of the model.

Which ASoC approach?According to what is men-tioned above,the behavior of the model entities may deals with several distinct concerns.It may be interesting to rely on paradigms which handle the separation of concerns (ASoC).In the following,we propose a quick overview on the possible ASoC approaches that may be use to specify the semantics of a model.

New programming paradigms appear such as AOP[19], SOP[14]or Generative Programming[9].In a certain way, 3They are experts of the domain and have to specify the know-how which is associated to it.the GOF book on design patterns[11]is dealing with this

problematic and proposes patterns to design applications

wmore generic and?exible.One of the most famous de-

sign patterns is the visitor;it separates the data structures(a

hierarchy of classes)and the associated treatments.Thanks

to visitors,treatments are written in a modular way(one

class)so that modi?cations and extension are easier to do.

The adaptable programming[23,30]has extended the

design pattern visitor.It provides a better?exibility to-

wards changes related to the data model.More precisely,

a traversal description language(a kind of extended pattern

matching model)makes possible to cut off from the under-

lying data structure of the application.

The design pattern visitor has been the basis of many

other research works[29].It is close from the concept of

multi-methods[4,25]or of generic functions for functional

programming.There are also other approaches which in-

troduce genericity within programming languages.We may

mention C++templates,generic libraries[26],generic Java

types[36]and programming by mixins[10].All of them

[27]need either,source code transformations,re?exivity,

meta-programming,or higher order techniques,to work out.

All the mechanisms mentioned above are not suf?cient

and AOP[19]represents one of the most interesting answer.

The main objective of this new paradigm,like the visitor de-

sign pattern,is to split up the application code into entities

(class,module)associated with a concern in order to ensure

a better application modularity.

To factorize and better capture semantics.According

to what has been suggested above our approach provides a

way to de?ne the semantics of each entity through the use

of a set of visitors that encapsulate all the concerns related

to it.In next paragraph we describe how this approach is

integrated in S MART T OOLS but let us provide some details

about new improvements that are undergoing speci?cation:?the use of declarative languages should be used in or-der to provide a support for the generation of the body

of actions.As a?rst approach this is OCL(Object

Constraint Language)that will be used and a classi-

?cation of assertions will be made in order to better

organize the speci?cation of the semantics and to en-

capsulate additional information.

?the speci?cation of actions should be improved in or-der to provide to the generator more information about the different concerns and the role of the actions;this should have an impact on the part of code of an action that can be automatically generated.The underlying know-how that we plan to use comes from the attribute grammar approaches[7,18].

?we propose to include several sets of meta-information which will address some key-points of the semantics of

the most interesting entities of the model.Let us take the example of one business model whose aim is to describe the operational semantics of object-oriented languages[8].Instead of trying to de?ne by hand the semantics of all kinds of classi?ers4of all languages, we prefer to extract a set of properties which allow to characterize each kind of classi?ers and to write generic actions which depend mainly on the value of those properties.

Thanks to these new capabilities we intend to improve the expressiveness of the meta-model in order to reduce the amount of code which has to be written when a model is de-scribed and to increase the impact of Generative Program-ming according to the speci?cation of the semantics of a model.

Implementation:the experience of S MART T OOLS.

In S MART T OOLS,we have created a generator that in-struments business models through the intensive use of the visitor design pattern.Thanks to the data model and pieces of meta-information about the semantic analysis (visit method signatures and traversal strategies),the gen-erator can produce a visitor by default that visits only the nodes included into the traversal strategies.When the model designer wants to associate a semantic analysis to a model, he only has to extend by inheritance the visitor de?ned by default and override some of the visit methods in order to specify the accurate treatment.

In S MART T OOLS,we have chosen to introduce AOP techniques which are designed especially for the meta-model which is dedicated to the description of semantic analyses(e.g.a type-checker or an evaluator).For its im-plementation,instead of using static source code transfor-mations or re?exive mechanisms,we choose to produce the code to be inserted.The integration of this capability into our semantic analyses is performed through an extension of the generator which has to produce also the speci?c aspect-plugging code.It is embedded into the visitor de?ned by default.Thanks to this extension the semantics analysis at-tached to one data model can be extended,not only by inher-itance,but also(dynamically)with aspects.Main advantage of such an approach is to provide AOP facilities which are i)close to the needs of the model designer,ii)easy to use: the resulting description of operational semantics is simple to understand,and iii)straightforward to implement so that potential evolutions of the needs of business models can be quickly integrated.

Let us now summarize and pay a particular attention on the implementation strong modularity.The handling of the semantics of business models is splitted into three distinct parts:the data model representation,the management of 4In UML this is the name used to address the concept of data type its recursive traversal and the semantic actions(the treat-ment)to be attached.Our choice to introduce a separa-tion of concerns even at the level of implementation favours easy model transformations and has an interesting impact on the ability of S MART T OOLS to support applications of the MDA approach.

https://www.wendangku.net/doc/17390542.html,ponent Models

The evolution of programming languages has also deeply changed the notion of modularity.Let us take some ex-amples such as ADA or Java packages,generic libraries in imperative programming,multi-inheritance and contract approach in Eiffel[24]or the“module”in functional pro-gramming[22].These different approaches provide inter-esting mechanisms in order to achieve more generic com-ponents but they are rather complex to use and they are not perfectly suitable for the needs of distributed applications. Many component technologies have been proposed in or-der to cope with these new needs:COM and DCOM for Microsoft,CCM for the OMG,and EJB for Sun.More re-cently,the Web-Services technology appeared with the pos-sibility to list the component services in catalogs(UDDI-Universal Description,Discover and Integration).

According to the state of the art,three of the main chal-lenges in component technologies are the followings:

?to extend the classical method-call.It allows to take into account the runtime environment(a three-tier ar-chitecture:the Internet,a message service,a database access)without any modi?cation of the business code;

?to extend the notion of interface.It provides a way to describe/discover the provided and required services

(e.g.the introspection in Java Beans)and to dynam-

ically adapt the interface(e.g.the multi-interface no-tion in CORBA);

?to add meta-information to a component.This is a generic approach to record information dealing with several concerns such as the deployment management, the security policy,etc.

These different mechanisms must be transparent towards the business code of the components.It corresponds to a kind of separation of concerns to avoid mixing the func-tional and the non-functional code.The OMG has proposed the MDA approach based on model transformations.It makes possible to get a better evolution of complex software applications towards component technologies[37].This bene?t explains the research efforts dealing with the def-inition of new generic component language and the links with both AOP and model transformations.

Implementation:the experience of S MART T OOLS.

The aim of S MART T OOLS is to de?ne new data model and to import existing model representations.In order to achieve this objective it is mandatory to have a component architecture which guarantees an easy evolution of the set of models handled by S MART T OOLS5.Moreover,having a component architecture(more precisely a meta-tool in the context of S MART T OOLS)allows to build also an applica-tion with only the required components.

The?rst step were to de?ne an abstract component model i.e.independent from any component technology. The issue is to be able to clearly identify the needs of S MART T OOLS.Without this model,these needs would have been hidden by the use of a component format which is non model-speci?c(e.g.IDL-Interface De?nition Lan-guage).Thanks to this component model,a generator can automatically produce the non-functional code,i.e.the con-tainer that hides all the communication and inter-connection mechanisms.For example let us take the broadcast mecha-nism which is used by a logical document and which aims to update the graphical views associated with it.This problem is totally transparent for the designer of application.Addi-tionally,it is very easy to adapt the architecture in order to introduce a new communication mechanism.

The second step were to de?ne a set of model transfor-mations(projections)from our abstract component model towards well-known component technologies such as web-services,CCM,or EJB(see?gure4).It makes easier the exportation of the produced components.

Eclipse

plug-in

https://www.wendangku.net/doc/17390542.html,ponent model transformations

Thanks to the experience gained by building projections, we do not believe that any of the three component technolo-gies mentioned above(Web-Services,CCM,EJB)would?t 5For example it will be crucial to handle the possible inter-connections between models.with our needs according to the component model itself and the speci?cations of connections between models.They are well appropriate for distributed applications but very poorly for applications with a generic(thus con?gurable)GUI. Moreover,the connection process proposed in S MART-T OOLS is much more?exible and dynamic than those of-fered by these technologies which are mainly dedicated to client/server architectures or Web servers.In S MART-T OOLS,component inter-connections are performed dy-namically when it is required.It also applies a pattern-matching on techniques on the names of services which are provided or required by the components in order to bind the connectors.

Another important aspect of our component model is that it is strongly linked with the meta-model which describes data models.This means that the components may be built knowing the data-model representation.The main conse-quence is the ability to exchange complex information be-tween two components such as sub-trees or path informa-tion(XPath)for the views and the associated logical docu-ment.The implementation of our model was rather easy.

We showed above that there are many advantages to create an abstract component model which?ts with the S MART T OOLS requirements rather than using a non-speci?c model.With the integration of an MDA approach (based on generative programming),we are able to produce implementations in different technologies(Platform Spe-ci?c Models).In this way,our models and the generated ones can evolve and be much better adapted.The immedi-ate result of this approach was to clearly identify the kernel6 of our tool.

Following our approach,the architecture of the produced applications are i)minimal(only the essential components may be deployed),ii)much more?exible,and iii)dynamic as new components can very quickly and at any time be plugged in.

6.Graphical User Interfaces

The graphical interfaces that make applications interac-tive must also be adaptable to their evolutions.Two main challenges,when designing a graphical interface,should be kept in mind:the interface might be executed on dif-ferent visualization devices and also be accessible through a Web interface.Moreover,the proliferation of new busi-ness models requires the ability to quickly design and im-plement interfaces(or pretty-printers)which are speci?c to one model or domain.In this context,visual programming can be very useful to build programming environments ded-icated to non-complex business models.

6Only0.5Mbytes.

Implementation:the experience of S MART T OOLS. One of the goal of S MART T OOLS,is to provide facilities for the development of new tools or programming environ-ments,especially for non-complex description languages. Its design takes into account the speci?cities of these lan-guages:i)they have their own data description language that should be accepted as input,and ii)the designers of such languages may not have a deep knowledge in com-puter science.Thus it was mandatory to establish a bridge with the Web semantics research topics,and to provide tools which are easy to use and which are built on well-known techniques.According to this context,it is possible to quickly implement an environment dedicated to a busi-ness model which may have one or more speci?c views of the documents.These different displays,more user-friendly and more readable than the XML format are ob-tained through a sequence of model transformations or re-?nements(see?gure5).

AST Concrete

syntax

tree

Tree of

graphical

objects

Tree of

graphical

objects

with styles

Figure5.Graphical view obtained by succes-

sive model transformations

A GUI can be considered as a tree of graphical objects (windows,tabs,panels,views,menu,etc.).According to this remark,the approach based on visitors mentioned in section4can be reused in order to generate graphical views. In the same way,all the abstract syntax tree manipulation methods(insert a node,remove a node,etc.)but also the implementation to obtain a view can be reused.For exam-ple?gure6shows three different views of the same GUI de-scription document:the generic XML display on the right, the generic hierarchical tree display on the left,and the main window of application.We have de?ned a simple GUI-speci?c model useful to con?gure the GUI according to the applications.

7.Related Works

Both our approach and S MART T OOLS are on the edge of different software engineering domains and many related research works.For those reasons we have preferred draw-ing up the main advantages of the approach instead of try-ing to compare both of them directly with their respective related works.We show the advantages of this approach ac-cording to the openness and evolutivity of the produced ap-plications more than to the qualities of S MART T OOLS itself. There is no doubt that on each concern of S MART T OOLS, the proposed techniques or solutions are certainly less pow-erful compared to equivalent research works or tools.For example our AOP approach is very speci?c to the models that are addressed by S MART T OOLS and cannot be com-pared directly with general approaches or tools such as As-pectJ[1,32].In the same way,it exists other research works on the design pattern visitor which presents different vari-ants of this design pattern[21,15,30].

It is necessary to keep in mind that the core of our ap-proach is to apply to different levels an MDA approach us-ing generative programming.The main bene?ts of this ap-proach are the followings:

?to handle different concerns homogeneously and si-multaneously.On the contrary,the usual component technologies mentioned earlier are mainly interested in the distribution concern.

?to remain on the implementation level.The UML modeling approaches[17,12,16]suffers from the gap between the speci?cation and implementation levels.?to produce generator-free source code,very close to hand-written programs.Very often,tools such as [6,20,18],introduce a strong dependence between the generator and the produced code.

?to be evolutive and open thanks to the use of stan-dard mechanisms(e.g.XSLT for program transforma-tion).For example according to program transforma-tion,there are many other tools available[20]but with proprietary input formats and interpretor engines that require additional work to plug in and use them.

?to treat the GUI or other environment facilities as sep-arated entities(components)that may or not,be inte-grated in the resulting application.This feature does not usually exist in the IDEs[2]that force the produced applications to be integrated into the IDE frameworks.

Finally,to make an exhaustive comparison with related works is almost impossible and is quite in opposition with the main objective of this paper.Indeed,as our approach gathers different domains,it exists,for each domain,many tools and research works related to our work that we should refer.We do not look for the best techniques for each con-cern but instead we want to show how different techniques can be integrated in a factory in order to obtain open and evolutive application.

Figure6.An example of S MART T OOLS GUI.

8.Conclusion

Trough the continuous development of S MART T OOLS, we are validating a new approach of software development mainly based on transformation and generation of models. We promote the idea that each concern of a model should be described by business models in order to better?t to the requirements.Moreover these models should be indepen-dent from the context of use,that is to say from existing technologies.Main bene?t is that these technologies should be able to evolve independently from the business model and vice-versa.New models based on new paradigms and new technologies are built thanks to generative program-ming.They represent either a re?nement of the input model (another PIM)or its implementation on a dedicated soft-ware platform(a PSM).

The main advantage of this approach is to make the evo-lution of models easy according to the software platform evolution or to the creation of new concerns.This evolution is performed only through modi?cations of the generator as-sociated with each models(data model,model of one spe-ci?c service,component model,GUI model,etc.).These generators contain the design methodologies(they repre-sent the software tool factory),they are customized thanks to input models,and they produce new intermediate models (they represent re?nements)or the?nal models adapted to the software platform.References

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SDN及ODL概括性总结

1、SDN是什么？ SDN(Software Defined Network)即软件定义网络，是一种网络设计理念。网络硬件可以集中式软件管理，可编程化，控制转发层面分开，则可以认为这个网络是一个SDN网络。SDN 不是一种具体的技术，不是一个具体的协议，而是一个思想，一个框架，只要符合控制和转发分离的思路就可以认为是SDN. 2、传统网络面临的问题？ 1）传统网络部署和管理非常麻烦，网络厂商杂，设备类型多，设备数量多，命令行不一致2）流量全局可视化难 3）分布式架构中，当网络发生震荡时，网络收敛过程中，有可能出现冗余的路径通告信息4）网络流量的剧增，导致底层网络的体积膨胀、压力增大；网络体积越大的话，需要收敛的时间就越长 5）想自定义设备的转发策略，而不是网络设备里面的固定好的转发策略 -------->sdn网络可以解决的问题 3、SDN的框架是什么 SDN框架主要由，应用层，控制层，转发层组成。其中应用层提供应用和服务（网管、安全、流控等服务），控制层提供统一的控制和管理（协议计算、策略下发、链路信息收集），转发层提供硬件设备（交换机、路由器、防火墙等）进行数据转发、 4、控制器 1）控制器概述 在整个SDN实现中，控制器在整个技术框架中最核心的地方控制层，作用是上接应用，下接设备。在SDN的商业战争中，谁掌握了控制器，或者制定了控制器的标准，谁在产业链条中就最有发言权 2）控制器功能 南向功能支撑：通过openflow等南向接口技术，对网络设备进行管控，拓扑发现，表项下

发，策略指定等 北向功能：目前SDN技术中只有南向技术有标准文案和规范，而北向支持没有标准。即便如此，控制器也需要对北向接口功能进行支持，REST API,SOAP,OSGI,这样才能够被上层的应用调用 东西向功能支持：分布式的控制器架构，多控制器之间如何进行选举、协同、主备切换等3）控制器的种类 目前市场上主要的控制器类型是：opendaylight （开发语言Java），Ryu(开发语言python), FloodLihgt(开发语言Java)等等 5、opendaylight（ODL）控制器介绍 ODL拥有一套模块化、可插拔灵活地控制平台作为核心，这个控制平台基于Java开发，理论上可以运行在任何支持Java的平台上，从Helium版本开始其官方文档推荐的最佳运行环境是最新的Linux（Ubuntu 12.04+）及JVM1.7+。 ODL控制器采用OSGi框架，OSGi框架是面向Java的动态模型系统，它实现了一个优雅、完整和动态的组件模型，应用程序（Bundle）无需重新引导可以被远程安装、启动、升级和卸载，通过OSGi捆绑可以灵活地加载代码与功能，实现功能隔离，解决了功能模块可扩展问题，同时方便功能模块的加载与协同工作。自Helium版本开始使用Karaf架构，作为轻量级的OSGi架构，相较于早前版本的OSGi提升了交互体验和效率，当然其特性远不仅仅于此。 ODL控制平台引入了SAL（服务抽象层），SAL北向连接功能模块，以插件的形式为之提供底层设备服务，南向连接多种协议，屏蔽不同协议的差异性，为上层功能模块提供一致性服务，使得上层模块与下层模块之间的调用相互隔离。SAL可自动适配底层不同设备，使开发者专注于业务应用的开发。 此外，ODL从Helium开始也逐渐完成了从AD-SAL（Application Driven Service Abstraction Layer）向MD-SAL（Model Driven Service Abstraction Layer）的演进工作，早前的AD-SAL，ODL控制平台采用了Infinispan技术，In?nispan是一个高扩展性、高可靠性、键值存储的分布式数据网格平台，选用Infinispan来实现数据的存储、查找及监听，用开源网格平台实现controller的集群。MD-SAL架构中采用Akka实现分布式messageing。 6、ODL的总体框架 ODL控制器主要包括开放的北向API，控制器平面，以及南向接口和协议插件。北向API 有OSGI和REST两类，同一地址空间应用使用OSGI类，而不同地址空间的应用则使用REST 类。OSGI是有状态的连接，有注册机制，而rest是无状态链接。上层应用程序利用这些北

todo与doing的区别

--- to do与doing的区另U 一般情况下，to do 是一般将来式,是打算去做什么（未做）;doing是现在进行式,是现在正在做什么，或（此事已做过或已发生、正做） like to do 和like doing 的用法有什么区别 简单的记忆方法。当表示喜欢，用like doing ，如：He likes cooking in his house. She likes singing. 表示爱好。 当表示想要，欲做某事（但还没进行）用like to do ，例如：He likes to cook in his house.- 他想在自己家做饭吃。 She likes to stay with us.- 她想和我们带一块儿。（但还没进行） 2 forget doin g/to do forget to do 忘记要去做某事。（未做） forget doing 忘记做过某事。（已做） The light in the office is stil on. He forgot to turn it off. 办公室的灯还在亮着，它忘记关了。（没有做关灯的动作） He forgot turning the light off. 他忘记他已经关了灯了。（已做过关灯的动作） Don't forget to come tomorrow. 别忘了明天来。（to come动作未做） 3 remember doin g/to do remember to do 记得去做某事（未做） remember doing 记得做过某事（已做） Remember to go to the post office after school. 记着放学后去趟邮局。 Don't you remember see ing the man before? 你不记得以前见过那个人吗？ 感官动词 see, watch, observe, notice, look at, hear, listen to, smell, taste, feel +doing表示动作的连续性，进行性 I saw him working in the garden yesterday. （强调”我见他正干活”这个动作） 昨天我见他正在花园里干活。

研究生自然辩证法考试题目及答案

自然辩证法复习题及答案 一、填空题 1、科学的三种类别。3′ 自然科学，社会科学，人文科学 2、科学技术的三种哲学反思。3′ 对科学进行辩护-捍卫科学；对科学进行批判-质疑科学；对科学进行审度-必要的转换 3、《自然辩证法》的学科内容和知识体系。4′ （1）自然观是人们对自然界的总体看法。它是从整体上研究自然界的本质及其发展规律的根本观点。 （2）科学技术观是人们对科学技术的总体看法。它是从整体上概括科学技术及其发展规律的根本观点。 （3）科学技术方法论是人们对科学技术所运用的认识和实践方法的哲学概括。它是关于科学技术研究中常用的一般方法的规律性理论。 （4）科学技术社会论是人们对科学技术的哲学反思。它是关于科学技术性质、作用（正、负）及其发展规律以及科学技术与社会的关系的总观点。 4、《自然辩证法》的学科由来和学科性质。2′ （1）由来：自然辩证法的历史源远流长，其萌芽形态可以上溯到古希腊的自然哲学，但作为一门独立学科则是由马克思和恩格斯在19世纪下半叶共同创立的。自然辩证法是近代自然科学的历史发展及其基本成就的科学总结，特别是十九世纪中后期自然科学最新发展和最新成就的科学总结，同时也是恩格斯本人多年刻苦学习和精心研究自然科学的科学总结。有关《自然辩证法》的材料是恩格斯1873─1886年这一时期写成的。整部著作没有写完，并且在恩格斯生前没有发表过。 （2）性质：自然科学、社会科学和思维科学相交叉的哲学性质的马克思主义理论学科 5、马克思主义自然观的三种类型。3′ 系统层次观，进化历史观，持续发展观 6、系统的基本特点。4′

整体性；层次性；有序性；动态性 7、“可持续发展”的概念。 既满足当代人的需求，又不对后代人满足其自身需求的能力构成危害的发展。 8、科学和技术的本质特征。2′ 科学：人对自然的理论关系、一般生产力。 技术：人对自然的实践关系、直接生产力。 9、四大产业体系的分类。4′ （1）第一产业体系（农、林、牧、畜、渔）； （2）第二产业体系（制造、采掘、建筑、运输）； （3）第三产业体系（通信、商业、金融、医疗、饮食、公共服务）； （4）第四产业体系（科学、文化、教育、咨询） 10、科学的五大解释。5′ （1）知识体系：发展着的认识 （2）认识活动：科学研究活动 （3）社会建制：科学家共同体 （4）思维方式：科学方法 （5）精神气质：科学精神 11、作为知识体系的科学的内容。4′ 科学事实、科学定律、科学假说、科学理论 12、科研选题的四个原则。4′ 需要性原则，创造性原则，科学性原则，可行性原则 13、获取科学事实的主要方法。2′ 科学观察方法；科学实验方法 14、科学实验的主要方法。4′ （1）纯化和简化研究对象（减法实验）：与隔离有关。 （2）强化和激化研究对象（加法实验）。 （3）再现和重演自然过程（过程模拟实验，乘法实验1）。 （4）替代物理过程和数学关系（结构模拟实验，乘法实验2） 15、整理科学事实的主要方法。4′

自然辩证法考试答案

自然辩证法 1.自然辩证法的性质、内容与方法 性质：自然辩证法是马克思主义的重要组成部分。 它的研究对象与研究范围：自然界-科学-技术-社会。 主要内容：自然观-科学观-技术观-科学技术与社会 研究方法： （1）科学问题的提出 （2）（2）科学事实的获取—观察与实验 （3）科学假说的形成 （4）科学理论的创立 科学思维方法—非演绎方法 ①分析与综合②归纳与概括③类比与联想④思想模型 2.近代唯物主义自然观的特点 (1)直观性：从某种有形的、直观的东西去寻求自然现象多样性的统一。用猜测和想象去说明自然现象； （2）辩证性：把自然界看成一幅由种种联系和过程交织起来的画面。 3.系统自然观、生态自然观的基本思想 系统自然观的基本思想 （1）自然界是一个系统.系统是由若干具有特定属性的组成元素经过特定联系而构成的、与周围环境相互联系的、具有特定的结构和功能的整体. （2）系统整体与部分的关系 系统的整体与部分之间的关系可以概括为两个方面： ①整体与部分相互依赖.整体是由部分组成的,整体不能脱离部分而独立存在. ②整体不等于部分之和.其具体表现在：整体大于部分之和（即所谓“三个臭皮匠,赛过一个诸葛亮”）；整体小于部分之和（即所谓“一个和尚挑水喝,两个和尚抬水喝,三个和尚没水喝”）. 生态自然观的基本思想 1）自然界是人类生存与发展的前提和基础,人是自然界发展的产物,人是自然界的一部分,人类的生存与发展依赖于自然界. 2）自然环境创造人,人也创造环境.人类的创造必须把改造自然与美化自然有机地结合起来,这样才是合乎人性的行为. 3）人要与自然和谐相处,自然环境与社会环境相统一.人要按自然规律办事,自然才会朝着有利于人类社会的方向发展否则,人类就会遭到自然的报复. 4）改革不合理的社会制度,是实现人与自然协调发展的重要途径,只有在共产主义社会才能真正实现人与自然的和谐统一.马克思主义关于“自然主义、人道主义、共产主义”相统一的生态思想揭示了生态自然观的本质. 5）可持续发展是既满足当代人的需要,又不对后代人满足其需要的能力构成危害的发展.它具有整体性、公平性和正义性等特点.人类是一个整体,可持续发展要求超越不同国家的文化和意识形态的差异,并采取联合的共同行动.生态文明所

todoanddoing用法

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2017自然辩证法考试试题及答案

1.什么是技术创新？它有哪些机制？ 技术创新 技术创新不同于技术发明，它主要是指技术成果在商业上的首次成功应用。技术创新包含技术成果的商业化和产业化，它是技术进步的基本形式。原始创新和集成创新是当前我国科技界和产业界关注的焦点所在，国家创新系统是市场经济架构下企业从事技术创新活动的环境。 技术创新的机制 技术创新的机制分为两个层次：国家层次是指国家创新体系，它主要是从国家竞争力考虑；企业层次主要是指，企业在其内部和外部各种因素的影响下，通过创新建立相应的组织结构，并对社会经济发挥作用的机理和原理，它主要是从企业竞争力考虑。 2.怎样正确地理解人与自然之间的矛盾和关系，谈谈你对中国可持续发展之路 的想法。 （1）人与自然的三重矛盾关系 自然资源和生态环境承载力的有限性与人民日益增长的物质文化需要的矛盾关系；尊重自然的价值与尊重人类发展权利的矛盾关系；技术开发与自然保护的矛盾关系。 （2）人与自然的关系 世界上的任何事物都是矛盾的统一体。我们面对的现实世界，就是由人类社会和自然界双方组成的矛盾统一体，两者之间是辩证统一的关系。一方面，人与自然是相互联系、相互依存、相互渗透的，人类的存在和发展，一刻也离不开自然，必然要通过生产劳动同自然进行物质、能量的交换。与此同时，人与自然之间又是相互对立的。人类为了更好地生存和发展，总是要不断地否定自然界的自然状态，并改变它；而自然界又竭力地否定人，力求恢复到自然状态。人与自然之间这种否定与反否定，改变与反改变的关系，实际上就是作用与反作用的关系，如果对这两种″作用″的关系处理得不好，极易造成人与自然之间失衡。 中国和世界正处在关键的十字路口。随着中国经济的快速发展，资源消耗以及随之产生的废物也大幅度增长，为了取得长期的经济增长，中国必须找到一条可持续发展之路。中国的环境恶化很严重，加上庞大的人口和前所未有的经济发展，这些都对中国走向可持续发展形成了重大障碍。这些都导致中国可持续发展的必然性：（一）人口方面的挑战（二）资源方面的挑战（三）生态环境方面的1、自然生态环境破坏日趋严峻2、自然生态环境污染日趋严峻：（1）水污染严重2)大气污染严重(3)土地污染严重(4)固体废物问题严重(5)噪声污染(6)电磁污染(7)光污染(8)热污染 在我国实施可持续发展必须做好以下几方面工作：首先要改变观念，科学认识自然，掌握自然规律，顺应自然发展，科学地协调、改造自然，善待自然，改变过去那种“先发展，后治理”的老路；其次要珍惜资源，节约资源；最后要唤起公众可持续发展意识，帮助人们树立正确的自然观。 中国走可持续发展道路是中国的必然选择，但这条道路同时是十分艰难的，首先经济实力薄弱是一大障碍，其次实现可持续发展需要科学技术特别是高新科学技术的支持，要达到这一点尚需长期努力，最后是地区发展的不平衡，尤其是西部地区水土流失等生态恶化现象更加严重。虽然有上述不足，但我们同时要看到，只要中国政府坚持发挥主导作用，充分运用科技力量，最广泛地动员公众参与，再加上国际社会的有力支持，随着经济体制改革、增长方式转变和科技进步的支持，中国可持续发展的前景是光明的 3.什么是科学精神？举例说明它的重要性。 科学精神是指从科学研究的过程和成果中所显示出来的科学本身所独有的一种精神气质，以及与之相应的科学思想、科学方法。它是科学价值的核心。科学精神有广泛而深刻的涵义，主要包括以下几个方面内容：

ODL之SDN入门篇

本文作为码农学ODL系列的SDN基础入门篇，分为两部分。第一部分，主要讲述SDN是什么，改变了什么，架构是什么样的，第二部分，简要介绍如何去学习SDN。 1.什么是SDN SDN(Software Define Network) ，即为软件定义网络，可以看成网络界的操作系统。从SDN的提出至今，其内涵和外延也不断地发生变化，越来越多的人认为“可以集中控制、开放可编程和转控分离的网络”就是SDN网络，并且还延伸出软件定义计算、软件定义存储以及软件定义安全等。SDN加快了新业务引入的速度，提升了网络自动化运维能力，同时，也降低了运营成本。SDN的基础

知识如下图所示，下面各小节内容将根据该图内容进行展开论述： 1.1.SDN基础 1.1.1.SDN本质及核心 我们知道，传统网络中的路由器也存在控制平面和转发平面，在高端的路由器或交换机还采用物理分离，主控板上的CPU不负责报文转发，专注于系统的控制；而业务板则专注于数据报文转发。所以路由器或交换机内的控制平面与转发平面相对独立又协同工作，如图所示：

但这种分离是封闭在被称为“盒子”的交换机或路由器上，不可编程；另一方面，从IP网络的维度来考虑，采用的是分布式控制的方式：在控制面，每台路由器彼此学习路由信息，建立各自的路由转发表；在数据面，每台路由器收到一个IP 包后，根据自己的路由转发表做IP转发； IP网络的这种工作方式带来了运维成本高、业务上线慢等问题，并越来越难以满足新业务的需求，传统上通过添加新协议、新设备等手段来缓解问题的方式，收益越来越少。穷则思变，许多人产生了革命的想法，现有的网络架构既然无法继续演进发展，为何不推倒重来，重新定义网络呢？真可谓“时势造英雄”，2006年斯坦福大学Nick McKeown教授为首的研究团队提出了OpenFlow的概念用于校园网络的试验创新，后续基于OpenFlow给网络带来可编程的特性，SDN （Software Defined Network）的概念应运而生。 SDN将原来封闭在“盒子”的控制平面抽取出来形成一个网络部件，称之为SDN 控制器，这个控制器完全由软件来实现，控制网络中的所有设备，如同网络的大脑，而原来的“盒子”只需要听从SDN控制器的命令进行转发就可以了。在SDN 的理念下，所有我们常见的路由器、交换机等设备都变成了统一的转发器，而所有的转发器都直接接受SDN控制器的指挥，控制器和转发设备间的接口就是OpenFlow协议。其简单模型如图所示：

常见的todo与doing

常见的“to do”与“doing”现象 有些动词后既可接to do，也可接doing，它们后接to do与doing在意思上有时有较大的差别。因为它们也是中考的常考点之一，因而我们应该搞清楚它们的区别。 1. stop to do/stop doing sth。 解析：stop to do sth.意为“停下来（正在做的事）去做（另外的）某事”，to do sth.在句中作目的状语。而stop doing sth.意为“停止做（正在做的）某事”。如Mary stopped to speak to me.玛丽停下（手头的工作）来跟我讲话。 When the teacher came in. the students stopped talking.老师进来时，学生们停止讲话。 2. remember to do/remember doing sth 解析：remember to do sth.意为“记住要去做某事”（还没有做）。而remember doing sth.意为“记得（已经）做过某事”如： Please remember to send the letter for me.请记住为我发这封信。 I don’t remember eating such food somewhere.我不记得在哪里吃过这种食物 3. forget to do/forget doing sth 解析：forget to do sth.意为“忘记做某事”（动作还没有发生）。而forget doing sth.意为“忘记做过某事”（动作已发生）。如： Don’t forget to bring your photo here.别忘了把你的相片带来。 I have forgotten giving the book to him.我忘记我已把书给了他。 4. go on to do/go on doing sth 解析：go on to do sth.意为“做完一件事，接着做另外一件事”，两件事之间有可能有某种联系。而go on doing sth.意为“继续做下去”。如： After reading the text, the students went on to do the exercises.学生们读完课文后，接着做练习。 It’s raining hard, but the farmers go on working on the farm.虽然天正下着大雨，但农民们继续在农场干活。 5. try to do/try doing sth 解析：try to do sth.意为“尽力去做某事”，而try doing sth.意为“（用某一种办法）试着去做某事”。如： Try to come a little early next time, please.下次请尽量早点来。 You can try working out the problem in another way.你可以试试用其它的方法解答这道题目。 6. can’t help to do/can’t help doing sth 解析：can’t help to do为动词不定式结构；can’t help doing sth.意为“身不由己地去做某事”或“情不自禁地去做某事。”如： We can’t help to finish it.我们不能帮忙完成此事。 I couldn’t help laughing when I saw her strange face.当我看到她奇怪的脸时，我情不自禁地笑了。 7. hear sb. do/hear sb. doing sth 解析：hear sb. do sth.意为“听见某人做某事”，指听到了这个动作的全过程；hear sb. doing sth.意为“听到某人做某事”，指听到时候，这个动作正在发生。如： I often hear him sing in the classroom.我经常听见他在教室里唱歌。 Do you hear someone knocking at the door?你听见有人在敲门吗？ 应该说明的是：和hear的用法一样的还有see、watch、notice等。

自然辩证法考试答案

自然辩证法题库 1.谈谈你对生态文明社会建设的具体设想 21世纪初是中国社会主义生态文明建设的关键阶段。改革开放以来，中国的社会主义生态文明建设取得了巨大成就，但社会主义生态文明建设的任务依然沉重。基于中国社会主义生态文明建设面临的困境与挑战，中国们必须继续坚持以人为本，以人与自然和谐共存为主线，以经济发展为核心，以提高人民生活质量为根本出发点，以体制创新为突破口，推动整个社会走上生产发展、生活富裕、生态良好的文明发展道路。 一是加强生态教育，提高全民族的生态道德素质。生态道德意识是建设社会主义生态文明的精神依托和道德基础。只有大力培育全民族的生态道德意识，使人们对生态环境的保护转化为自觉的行动，才能解决生态保护的根本问题，才能为社会主义生态文明的发展奠定坚实的基础。因此，建设社会主义生态文明，必须把道德关怀引入到人与自然的关系中，树立起人对于自然的道德义务感，养成良好的“生态德性”。尤其要抓好学校教育的环节，特别要重视青少年生态道德意识的培育和提高，帮助学生树立环境生态观念、环境资源观念、环境道德观念。 二是改革生产方式，做强生态产业。对现行的生产方式进行生态化改造是推进社会主义生态文明建设的重要手段。现阶段发展生态产业的重点，是要建立起资源节约、环境少污染型的国民经济体系，走生态农业、生态工业的发展道路。要下决心关停并转那些能源消耗大、经济效益差、环境污染重的企业。发展生态农业，主要包括绿色农业食品和绿色食品原料，生态林业、草业、花卉业，生态渔业，观光农业，生态畜牧产品，生态农业手工业等方面。为此，要研究开发生态技术，防止土壤肥力退化，进行植物病虫害综合防治，实现生活用能替代和多能互补、废弃地复垦利用和陡坡地退耕还林，发展山地综合开发复合型生态经济、以庭院为主的院落生态经济，以及农村绿色产业和绿色产品，提高农业产业化水平，促进农村生态经济的发展。另外，还要重视生态旅游业和环保产业的发展。 三是实施生态工程，全面推进生态环境的保护和治理。生态工程是社会主义生态文明建设的重要组成部分。结合中国的自然、经济和社会特点，“十五”期间，应重点解决危害人民群众身体健康、社会最为关心的环境问题：一要加强城乡饮用水水源地保护，加强工业废水和城市污水的生态处理，抓好重点流域、区域、海域的污染防治工作；二要抓好退耕还林还草和植树造林工程，特别是北京地区风沙源治理、天然林保护和沿海防护林等生态工程建设；三要防治大中城市空气污染、危险废物污染，防止生态破坏； 四要加快自然保护区、环境优美城市和生态省（市、自治区）的创建工程；五要继续推进计划生育的基本国策，提高全社会的计划生育意识，确保控制人口数量，确保提高人口质量；六要在鼓励使用可再生资源的同时，控制可再生资源的利用率不能超过其再生和自然增长的限度，提倡少用或不用不可再生资源，防止资源骤减，力争全面推进生态环境的保护和治理。 四是完善社会主义生态文明建设的政策体系和法律体系。社会主义生态文明建设不仅需要道德力量的推动，也需要政府和权力机关出台必要的政策、制定相关法律法规来进行硬约束。要建立综合决策制度，用政府的权威保证生态环境免遭破坏。特别是在制定规划、计划及重大经济行为的拟议过程中，充分发挥政府综合决策的作用，把生态环境目标和经济发展目标结合起来、统筹考虑，以从源头上解决对生态的危害问题。要适时出台相关政策，用宏观调控手段引导生态建设的积极性。包括：引导生态型项目开发的扶

todo和doing的差别

To do 和 doing的用法 1. finish, enjoy, feel like, consider, imagine, keep, postpone, delay, mind, practise, suggest, risk, quit+doing 2. 1）forget to do 忘记要去做某事（此事未做） forget doing忘记做过某事（此事已做过或已发生） 2）stop to do 停止、中断（某件事），目的是去做另一件事 stop doing 停止正在或经常做的事 3）remember to do 记住去做某事（未做） remember doing记得做过某事(已做) 4) regret to do对要做的事遗憾 regret doing对做过的事遗憾、后悔 5）try to do努力、企图做某事 try doing试验、试一试某种办法 6) mean to do打算，有意要… mean doing意味着 7）go on to do 继而（去做另外一件事情） go on doing 继续（原先没有做完的事情） 8）propose to do 打算（要做某事） proposing doing建议（做某事） 9) like /love/hate/ prefer +to do 表示具体行为；+doing sth 表示抽象、倾向概念 （注)如果这些动词前有should一词，其后宾语只跟不定式，不能跟动名词。例如： I should like to see him tomorrow． 10) need, want, deserve +动名词表被动意义；+不定式被动态表示“要(修、清理等)”意思。 Don’t you remember seeing the man before你不记得以前见过那个人吗 You must remember to leave tomorrow．你可要记着是明天动身。 I don’t regret telling her what I thought．我不后悔给她讲过我的想法。(已讲过) I regret to have to do this， but I have no choice．我很遗憾必须这样去做，我实在没办法。(未做但要做) You must try to be more careful．你可要多加小心。 Let’s try doing the work some other way．让我们试一试用另外一种办法来做这工作。 I didn’t mean to hurt your feeling．我没想要伤害你的感情。 This illness will mean (your) going to hospital．得了这种病(你)就要进医院。 3.省to 的动词不定式 1）情态动词 ( 除ought 外，ought to)： 2）使役动词 let, have, make： 3）感官动词 see, watch, look at, notice , observe, hear, listen to, smell, feel, find 等后作宾补，省略to。 注意：在被动语态中则to 不能省掉。 I saw him dance.

自然辩证法考试参考答案

自然辩证法概论复习题 1、论技术创新：科学技术与经济的有效结合。 科技与经济相结合，就是强调科技发展要与经济发展相结合。“科学技术是第一生产力”是邓小平科技思想的核心，这一论断说明了科学技术决定着生产力发展的方向、规模和速度，要发展生产力就必须依靠科学技术。只有经济发展了，才可能有生产力的飞速发展。因此，科学技术进步和经济发展成为推动生产力发展的两大重要支柱，发展生产力需要科技与经济的有机结合。 自邓小平提出科技与经济结合这一论断开始，中国就在推进结合的过程中不断发展，几十年来也取得了一些成就，但是不能忽视结合的不彻底，以及存在的种种问题。如今，中国发展进入创新驱动的新阶段，科技与经济结合的问题再次成为焦点，要做好这项工作，必须以更符合创新规律的方式来推动。在对结合的认识上，不仅要加深对其重要性的理解，增强全民科技意识，将结合问题看作科技界的问题，也要看作经济界的问题，切实转变经济工作的根本理念，体现创新的重要性。我们更应该明确技术创新的经济属性，从产业链的高端位置入手，获得高价值。此外，现阶段我国的新产品主要应用者不能依赖于国外市场，应该发挥本国市场对自主创新活动的牵引作用，将市场应用作为自主创新实践不可或缺的环节。另外，资本市场对推动科技与经济结合也至关重要。硅谷的成功不仅仅因为有一流的技术，更是因为有一流的技术与资本对接的机制。从中国的现实来看，尽管开办了创业板，但真正对技术创新的支持还远远不够，短期利益导向严重阻碍了科技与经济结合。当前，在政府资金越来越充裕的条件下，应该下大力气引导投资市场关注科技与经济结合，关注创新型企业培育，形成鼓励创新的投资市场。 或者 社会经济对科学技术发展的影响？ 答：A社会的经济需求是科学技术发展的最重要的推动力量； B社会的经济支持是科学技术发展的最重要的物质基础； C社会的经济竞争是科学技术发展的最重要的刺激因素； D经济对科学技术的影响还集中体现在生产的影响上。 技术创新：技术创新是一个从产生新产品或新工艺的设想到市场应用的完整过程，它包括新设想的产生、研究、开发、商业化生产到扩散这样一系列活动，本质上是一个科技、经济一体化过程，是技术进步与应用创新共同作用催生的产物，它包括技术开发和技术应用这两大环节。 技术创新的主要原则： 1、技术上的新颖性或创造性。技术创新特征在技术上的体现就是“新颖”，它是指在一定时期和市场范围内，相对于原有技术的改进或创造。2、经济上的高风险性和高收益性。技术创新是一项充满风险的事业，但这并不妨碍人们去创新，这是因为创新存在极高的回报。3、技术创新的中介性或过渡性。作为科技发展与经济增长中间环节的创新具有中介性，是技术与经济。 2、从生态自然观的产生说明这种自然观是对辩证唯物主义自然观的丰富的发展？ （1）马克思、恩格斯的生态思想是现代生态自然观的直接的理论来源。马克思、恩格斯的生态思想：①自然界是人类生存和发展的前提和基础；②环境创造人，人也创造环境；③自然生产力是社会生产力的基础；④人要与自然和谐一致。⑤改革不合理的社会制度，是实现人与自然协调发展的重要途径。 （2）以生态科学为基础的生态自然观是当代人类对“生态危机”进行反思和对生态科学进行概括与总结的结晶。“生态危机”是指由于人类不合理的活动，在全球规模或局部区域导致生态过程即生态系统的结构和功能的损害、生命维持系统瓦解，从而危害人的利益、威胁人类生存和发展的现象。其表现为：人口激增、自然资源消耗、短缺、环境污染。 （3）生态自然观的基本思想： ①生态系统是生命系统；②生态系统具有显著的整体性；③生态系统是自组织的开放系统； ④生态系统是动态平衡系统；⑤生态系统是稳定性与变化性相统一的平衡。 生态自然观是对马克思、恩格斯生态思想的继承与发展，是在人类反思全球性“生态危机”的过程中和总结现代生态科学的最新思想成果的基础上形成的。 3、根据选题的基本原理，在你的专业上选一个题，并简述选题的过程和注意事项。 所谓科研选题,从狭义上来讲,是指选择和确定所要研究解决的课题,从广义上来说, 它包括确定研究方向和选择研究课题两个方面。研究课题是指科学技术领域中尚未解决的科学问题。—而研究方向是指研究者在一个较长时期内从事研究活动的领域。 选题的过程 (一)课题调研和实际考察。

OpenDaylight与Mininet应用实战之复杂网络验证(五)

OpenDaylight与Mininet应用实战之复杂网络验证（五） 1多交换机的测试 Mininet中本身就支持多交换机网络拓扑的模拟创建，可通过Python API自定义拓扑创建满足使用者在仿真过程中的多方位需求。 下面举出具体示例验证多交换机支持： 执行此条命令后，查看ODL的Web界面显示的网络拓扑。界面拓扑显示如下： 对所有的虚拟host之间进行互ping操作，通过pingall命令，验证主机间的连通性，继而可验证支持多交换机的功能。

由pingall显示的结果可看出，主机间能够互相通信，且将数据包的流转发给交换机，并由交换机上报给ODL控制器来下发流表使主机通信。 主机通信过程中可查看交换机的流表信息及本身信息。 由交换机流表信息显示可知，控制器通过策略将流表下发到交换机中，使主机发出的数据包转发到下一目的地址。每个交换机查看信息的端口都不同，从第一个交换机端口号为6634开始，以后每一个交换机依次在之前交换机端口号的基础上加1，如第二个交换机的端口为6635。其他交换机的流表信息及自身设备信息可根据此说明进行查看。 2多控制器的测试 多控制器验证支持测试包括两种情况： ■OpenFlow网络中多个同一类型的控制器； ■OpenFlow网络中多个不同类型的控制器； 2.1多个同一类型的控制器验证 测试OpenFlow网络中多个同一类型的controller，比如OpenDaylight，多个ODL之间通过

OpenFlow1.0协议标准交互。 通过Mininet验证，在Mininet中模拟创建的OvS交换机不能指定连接多个控制器，且在同一个Mininet中创建的多个交换机不能指定不同的控制器。所以在验证交换机被多个同一类型的控制器管控时，不能通过用Mininet来验证，但是可通过真实交换机来验证。 如，在真实交换机中设置连接此文中的ODL控制器及另一个ODL控制器，命令为： 连接两个相同类型的ODL控制器，其中192.168.5.203为上述实验使用的控制器，192.168.5.111为另外安装使用的ODL控制器。通过执行如下命令查看交换机连接的控制器信息。 is_connected:true表示交换机都成功连接上控制器。交换机连接到这两个控制器后，控制器通过设备拓扑管理也可以发现此交换机，同时控制器管控存在主备关系，但控制器都可对交换机进行管控、下发流表等操作。 通过真实OpenFlow交换机连接多个控制器，可以实施，且已经验证，控制器和控制器之间存在主备关系，多控制器都可以对连接的交换机进行管控。 2.2多个不同类型的控制器验证 在OpenFlow网络中多个不同类型的controller，比如同时存在NOX和ODL，它们之间如果遵循OpenFlow协议标准的话，也是能够协作工作的。多个不同类型的控制器管控交换机与2.1小节是同样的道理。 如，在真实交换机中设置连接此文中的ODL控制器及其他另一个不同类型的控制器，如POX，命令为： 连接两个不同控制器，其中192.168.5.203为上述实验使用的控制器，192.168.5.111为另外安装使用的POX控制器。经试验验证，ODL与POX都遵循OF1.0版本的协议标准，所以在复杂网络多控制器情况下，只要控制器遵循相同的标准规范，控制器之间可进行对网络的通信管理等。此处实验结果与2.1节一致。交换机连接这两个控制器后，控制器管控存在主备关系，但控制器都可对交换机进行管控、下发流表等操作。 3总结 本文主要对复杂网络多交换机及多控制器的支持验证。因Mininet现在无法模拟多控制器管控一个交换机的情况，所以本专题还是侧重对多交换机的管控实验。至此，OpenDaylight 与Mininet应用实战专题将结束，有介绍不到位或者有疑问的地方请多多指教，互相交流。谢谢！

doing,todo,do的用法

一．To do形式 afford to do sth. 负担得起做某事 agree to do sth. 同意做某事 arrange to do sth.安排做某事 ask to do sth. 要求做某事 beg to do sth. 请求做某事 care to do sth. 想要做某事 choose to do sth. 决定做某事 decide to do sth. 决定做某事 demand to do sth. 要求做某事 expect to do sth. 期待做某事 fear to do sth. 害怕做某事 help to do sth. 帮助做某事 hope to do sth. 希望做某事 learn to do sth. 学习做某事 manage to do sth. 设法做某事 offer to do sth. 主动提出做某事 plan to do sth. 计划做某事 prepare to do sth. 准备做某事 pretend to do sth. 假装做某事 promise to do sth. 答应做某事 refuse to do sth. 拒绝做某事 want to do sth. 想要做某事 wish to do sth. 希望做某事 happen to do sth. 碰巧做某事 struggle to do sth. 努力做某事 advise sb. to do sth. 建议某人做某事allow sb. to do sth. 允许某人做某事 ask sb. to do sth.请（叫）某人做某事bear sb. to do sth.忍受某人做某事 beg sb. to do sth. 请求某人做某事cause sb. to do sth. 导致某人做某事command sb. to do sth. 命令某人做某事drive sb. to do sth .驱使某人做某事elect sb. to do sth. 选举某人做某事encourage sb. to do sth. 鼓励某人做某事expect sb. to do sth. 期望某人做某事forbid sb. to do sth. 禁止某人做某事force sb. to do sth. 强迫某人做某事 get sb. to do sth. 使（要）某人做某事hate sb. to do sth. 讨厌某人做某事 help sb. to do sth. 帮助某人做某事

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