A high degree of abstraction and capacity for reuse can be obtained in software design through the use of Generic Programming (GP) concepts. Despite widespread use of GP in computing, some areas such as the construction of generic component libraries as the skeleton for complex computing systems with extensive domains have been neglected. Here we consider the design of a library of generic components based on the GP paradigm implemented with Java. Our aim is to investigate the feasibility of using GP paradigm in the construction of complex computer systems where the management of users interacting with the system and the optimisation of the system’s resources is required.Postprint (author's final draft

Caballé Llobet, Santiago

Xhafa Xhafa, Fatos

English

A high degree of abstraction and capacity for reuse can be obtained in software design through the use of Generic Programming (GP) concepts. Despite widespread use of GP in computing, some areas such as the construction of generic component libraries as the skeleton for complex computing systems with extensive domains have been neglected. Here we consider the design of a library of generic components based on the GP paradigm implemented with Java. Our aim is to investigate the feasibility of using GP paradigm in the construction of complex computer systems where the management of users interacting with the system and the optimisation of the system’s resources is required

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A study into the feasibility of generic programming for the construction of complex software

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A Study into the Feasibility of GenericProgramming for the Construction of ComplexSoftwareSanti Caballe´1 and Fatos Xhafa21 Open University of Catalonia, Department of Information SciencesAv. Tibidabo 39-43, 08035 Barcelona, Spainscaballe@uoc.edu2 Polytechnic University of Catalonia, Campus Nord C6Jordi Girona 1-3, 08034 Barcelona, Spainfatos@lsi.upc.esAbstract. A high degree of abstraction and capacity for reuse can beobtained in software design through the use of Generic Programming(GP) concepts. Despite widespread use of GP in computing, some areassuch as the construction of generic component libraries as the skeleton forcomplex computing systems with extensive domains have been neglected.Here we consider the design of a library of generic components based onthe GP paradigm implemented with Java. Our aim is to investigate thefeasibility of using GP paradigm in the construction of complex computersystems where the management of users interacting with the system andthe optimisation of the system’s resources is required.1 IntroductionIn traditional forms of engineering we find that productivity, quality and cost aresuch important factors in industrial processes that the very survival of companiesdepends upon them. For this reason, great efforts have been made to improvethe techniques, methods and tools which are available for product developmentand the results have clearly been spectacular. However, in the case of softwaredevelopment similar progress has not been made so far even though there is noessential difference with other forms of engineering. In explaining why this is sowe need to remember that the technology is more recent and that the product ishighly complex, but the key is doubtless to be found in the fact that the conceptof reusability has not been sufficiently exploited.The reuse of previously created product parts leads to reduced costs and im-proved productivity and quality to such an extent that industrial processes willtake a great leap forward. In all advanced forms of engineering we can observethat new products are usually developed by reusing tried and tested parts butin software engineering it seems that new products are almost always developedfrom scratch. To benefit from the advantages of reusability it is necessary todevelop better methodologies such as Generic Programming (GP) that facilitatethis possibility. GP when applied in the context of computer software develop-ment is an innovative paradigm that attempts to make software as general aspossible without losing efficiency. It achieves its goal by identifying interrelatedhigh-level family from a common requirement set. By the application of this tech-nique, especially in design phases, software is developed offering a high degreeof abstraction which is applicable to a wide range of situations and domains.2 Generic Programming ObjectivesBy applying GP to develop computer software we achieve important objectives:Reuse. This is the main reason for applying GP ideas. The real objective,however, is to be able to reuse and extend software components widely so that itadapts to a great number of interrelated problems. This concept of reutilizationis much broader than has been seen until now.Quality. Due to the great potential for reutilization of GP, it is necessaryto guarantee maximum quality. Here ”quality” refers to the correctness androbustness of implementation which provides the required degree of reliability.Furthermore, GP provides innate reliability as the implementations are nothingmore than skeletons, without details, and as such are simpler to construct duringthe codification phase and hence can be produced with minimal errors.Efficiency. As in the case of the quality, we also have to guarantee the effi-ciency of components as if this not done the performance repercussions will benoted, just as with lack of quality, in all of the systems involved.Productivity. Inherent to reutilization is the saving through not having tocreate software components again that already exist. Hence, there is an increasein computing production–one of the benefits that GP seeks in order to bring theproduction potential of computing applications as in other industries.Automatisation. Here the aim is to automatise the processes so that generalrequirements with a high level of abstraction and specially designed tools canbe used to produce operative programmes. GP provides the skeleton for theinitial generic requirements. The resulting programme will be the base for othermore specific programmes which in turn will construct others following a cascadeprocess so giving us a more solid base permitting more automatisation.Personalisation. As the general requirements are made more particular, sothe product that is generated becomes more optimised to meet the specificneeds of the client. GP intervenes largely in a first phase of this abstraction-specialisation/personalisation cycle by identifying the abstractions and supply-ing a first level of specialisation; this is a great challenge of the software industry.3 Statement of the ProblemThe development of applications based on GP not only has the practical advan-tage of improved productivity but also results in software that is more robustand reliable. Considerable research has already been done into the constructionof libraries of generic data structures based entirely on GP (Standard TemplateLibrary [1] and Data Structures and Algorithms in Java [2]) but very little hasbeen done into the development of computer systems.As a contribution to filling this gap, we consider the construction of a li-brary (see API at: http://cv.uoc.edu/∼scaballe/tfc/api) of components of greatlygeneric use that creates the skeleton for the construction of complex systemsrequiring the management of the users interacting with the system and opti-misation of the system’s resources. The aim of this study is to investigate thefeasibility of the design of generic software as the basis of complex and extensive-domain computer systems. The library is based on the GP paradigm as the aimis to encourage the greatest possible reusability of its own generic componentsfor the development of the specific computer systems highly complex. Our firststep is to identify those parts which are common to most applications of thisdomain and we then proceed to isolate the fundamental parts in the form of ab-stractions from which the basic requirements have been obtained. Once a logicaldivision into components and subsystems has been made, we analyse and designeach component separately employing OO methodology. In order to maintainintact the ideas of GP design that are found, we implement an implicit logicallayer that creates a correspondence between the GP design and the OO design.Since Java has a great predisposition to adapting and correctly transmittinga high degree of abstraction and make the software reusable, this library hasbeen implemented in this programming language.As we will demonstrate, the advantages that GP offers with regard to quality,efficiency, productivity and so on provides a solid basis for the construction ofspecific software that is faster, more efficient and highly reliable.4 Design of the LibraryThe library is made up of three components which constitute the skeleton of thebasic structure of whatever application is constructed using this library.The Users component. It is made of two subsystems: (a)GenericUserManage-ment. It administers the basic elements participating in the administration ofthe users of a computing system(see Fig. 1). The key entity GenericUser repre-sents a person, group, device, etc., which is able to have multiple identities/roles.An Identity is unique both at user level and within the group of all the users ofthe system. An Authenticator is made up of both public and private keys andit may be used to validate each identity. (b) UserProfileManagement. It ad-ministers users’ preference information which is obtained through the elementsof the profile, the sum of all of these ElementProfile forms the UserProfile.The Security component. It is made up of two subsystems: (a) Authentication-Management. It identifies the user and manages the log in and log out proce-dures. The generic process of authentication consists of starting a UserSessionin which a user’s identity and authenticator are validated. (b) Authorisation-Management. It administers the system’s security policy. This information willmanaging the data and which will allow the treatment of both ordinary textsand the database during particularisation.A complete hierarchy of exceptions has been created to capture and treaterrors and anomalous situations that are not foreseen in the specification andwhich come to light whilst working with each component. These exceptions givea high degree of reliability to applications built with the components withouthaving to depend on the error treatment of the specific platform.5 An Application: Use of the Library in ConstructingDistributed Applications for Collaborative LearningWe have gained experience in GP paradigm by using our library as the base forconstructing complex applications within the domain of the library itself.We are currently working on the development of a prototype of a collab-orative workspace as a distributed and decentralised application (this kind ofdistributed applications are discussed in [7]) aiming to facilitate working groupsas well as asynchronous groupware coordination tasks in the context of ProjectBased Collaborative Learning. The main objective is to create web-based sharedworkspaces where the users of each space are able to deposit, receive and share alltypes of resources permitting full synchronous and asynchronous communicationwithout depending on the computer platform being used. The system permitsthe identification and the notification of recent events to each shared workspaceuser and the consultation of the system events history in order to extract statis-tics about any time period of the system’s life. Furthermore, the system permitsthe control of user access to valuable resources by allocating roles and privilegesto all system users.Due to the high degree of interaction between users and the system (andparticularly the fact that the events are widely spread) and the necessity tocontrol and optimise the system’s resources (with minimum storage), we can seethat the system domain forms part of library’s domain showing that the libraryis clearly reusable in this area. What distinguishes our system from existingclient/server environments such as BSCW [8] is the strong decentralisation of thesystem which has great advantages in terms of the increased hardware resources,high performance, lower cost and strong scalability which are all essential factors.In order to decentralise the system, a P2P architecture has been designedespecially for document sharing (text, audio, etc.) among the users. On the otherhand, the system resources index and the system administration in general (userauthentication, system’s events management, etc.) is centralised in a single pointas attempting decentralise this part provoked a worse behaviour of the systemin terms of the document location, user management, system security and so on.During our application construction, we have checked how even in designphases our library adapts perfectly thanks to a good matching of those genericentities proposed with the instantiation of those we have made here. We can see,for example, how GenericUser matches with whatever user type is found in acollaborative work environment (single users, groups, etc.) and Identity becomesthe unique identifier of the user (e-mail address) and also we can check howElementLog gathers all the information needed to identify the system’s eventsfrom which it is possible to carry out their notification to the rest of the users.With regards to functionality, the generic processes are also well-matched withspecific ones such as AutenticationValidation, which once instantiated, permitscarrying out user authentication and accessing to their own workspace.The user interface is instantiated in a graphic mode taking advantage of thegenericity of the library. Regarding the persistence, GenericDiskManager ab-straction is available and its specialisations which represent a bridge that keepsthe logic of the application independent from its data allowing persistence in dif-ferent models, which in our case will be Scalable Distributed Data Structures [6].During the design of the decentralisation, we have checked that our library isnot totally reusable with respect to persistence as it was not designed for this aim.A generic data structure interface needs to be designed which will permit data tobe distributed and located within a scalable, consistent and fault-tolerant context(the latter basically through data replication). Even so, thanks to the great GPabstraction capacity, it permits one more grade of genericity to be imposed inthe library so preparing it for distributed and centralised environments.Conclusions and Ongoing Work. In this study we have shown the feasibilityof generic programming for the construction of complex software within a spe-cific but extensive domain. We would like to assess the performance of genericcomponents when specialised in specific systems (e.g. distributed systems overthe Grid) and to estimate their development cost. We will also investigate otherfacets of GP such as design patterns and generic exception handling and provideanother version of our library for distributed and decentralised environments.Acknowledgments. This work has been partially supported by the SpanishMCYT project TIC2002-04258-C03-03.References1. Musser, D., Derge, G., and Saini, A: The STL Tutorial and Reference Guide. C++Programming with Standard Template Library. Addison-Wesley, 20022. Goodrich, M. and Tamassia, R.: Data Structures and Algorithms in Java. Willey20013. Alexandrescu, A.: Modern C++ Design: Generic Programming and Design PatternsApplied. Addison Wesley, 20014. Bloch, J.: Effective Java Programming Language Guide. Addison-Wesley, 20015. Kreft, K. and Langer, A.: Combining OO Design and Generic Programming 1997.http://www.langer.camelot.de/Articles/OOPvsGP/Introduction.htm6. Litwin, W.: SDDS: Scalable Distributed Data Structures, 2000.http://ceria.dauphine.fr/SDDS-bibliograhie.html7. Borghoff, U.M and Schlichter, J.H.: Computer-supported cooperative work: intro-duction to distributed applications. Springer, 2000.8. Bentley R., Horstmann T. and Trevor J.: The World Wide Web as Enabling Tech-nology for CSCW: The case of BSCW. Computer-Supported Cooperative Work:Special issue on CSCW and the Web, Vol. 6. 1997 Kluwer.

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A study into the feasibility of generic programming for the construction of complex software

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