- Количество слайдов: 28
Component Based Development R&D SDM 1 2010 Theo Schouten
Content • • • Component Based Development, what is it Engineering of Component Based Software Development Domain Engineering Component Based Development Standard Software packages book chapter 30 Component-Based Software Engineering 7 th ch 10 Component level design
Elements of CBD • Reuse of software components • Buy, don’t develop – ‘Commercial off-the-shelf’ (COTS) • Shift of attention: – From programming to composing – From design to selection • Speed of development • Cost efficient
History • functions (subroutine) in first “high level” programming languages, provided reuse in libraries – LINPACK, EISPACK (1970’s), LAPACK (1992 -now) • Object Oriented languages – reuse of classes and sets thereof • 1968 Douglas Mc. Ilroy “Mass Produced Software Components” – leaded to pipes and filters in Unix • 1986 Brad Cox Objective-C – strict superset of C with Smalltalk-style messaging – Steve Job, NEXT, Mac OS X, Cocoa API – became very popular last year (see TIOBE)
Origin CBD (or CBSE) • Component-based software engineering (CBSE) is a general approach to software development that is based on software reuse. • It emerged from the failure of object-oriented development to support effective reuse. Single object classes are too detailed and specific. • Components are more abstract than object classes and can be considered to be stand-alone service providers.
Definitions ‘Component Based Software Engineering (CBSE) is changing the way software systems are developed. CBSE embodies the ‘buy, don’t build’ philosophy…… CBSE shifts the emphasis from programming software to composing software systems. Implementation has given way to integration as the focus. At its foundation is the assumption that there is sufficient commonality in many large software systems to justify developing reusable components to exploit and satisfy that commonality’ Clements 1995
What is a Component? • OMG Unified Modeling Language Specification [OMG 01] defines a component as – “… a modular, deployable, and replaceable part of a system that encapsulates implementation and exposes a set of interfaces. ”” • OO view: a component contains a set of collaborating classes • Conventional view: a component contains processing logic, the internal data structures that are required to implement the processing logic, and an interface that enables the component to be invoked and data to be passed to it.
CBSE essentials • Independent components specified by their interfaces. • Component standards to facilitate component integration. • Middleware that provides support for component interoperability. • A development process that is geared to reuse.
Design principles • • Components are independent, no interference Component implementations are hidden Communication is through well-defined interfaces Container: service provider for locating and getting component interface Implementation Interface Component Container
Component models • A component model is a definition of standards for component implementation, documentation and deployment. • Examples of component models – EJB model (Enterprise Java Beans) – COM+ model (. NET model) – OMG Corba Component Model • The component model specifies how interfaces should be defined and the elements that should be included in an interface definition.
OMG/ CORBA • The Object Management Group has published a common object request broker architecture (OMG/CORBA). • An object request broker (ORB) provides services that enable reusable components (objects) to communicate with other components, regardless of their location within a system. • Integration of CORBA components (without modification) within a system is assured if an interface definition language (IDL) interface is created for every component. • Objects within the client application request one or more services from the ORB server. Requests are made via an IDL or dynamically at run time. • An interface repository contains all necessary information about the service’s request and response formats.
Sun Java. Beans • The Java. Beans component system is a portable, platform independent CBSE infrastructure developed using Java • It encompasses a set of tools, called the Bean Development Kit (BDK), that allows developers to – analyze how existing Beans (components) work – customize their behavior and appearance – establish mechanisms for coordination and communication – develop custom Beans for use in a specific application – test and evaluate Bean behavior.
Microsoft COM • The component object model (COM) provides a specification for using components produced by various vendors within a single application running under the Windows operating system. • COM encompasses two elements: – COM interfaces (implemented as COM objects) – a set of mechanisms for registering and passing messages between COM interfaces.
Documents Steps Phases Decision place in classical development Phase 1 Definition Phase 2 Design Phase 3 Realize Phase 4 Implement Questions: - Is COTS available to fulfill the requirements ? - Are internally developed modules suitable? - Are the interfaces of the components compatible with the architecture? Vaststellen Systeem Behoeften Definitie studie Haalbaarheids Rapport Functioneel Ontwerp No Functionele Specificatie Requirements Analysis Technisch Ontwerp Technische Specificatie Yes Component Based Development 14
Engineering of CBS • This should fill in the following aspects: – Identifying the components which are candidates for implementation – Qualifying the interfaces of the components – Adapting of the components to the architecture – Updating of the components due to changes in the requirements. • CBSE Process: – Domain Engineering: Library Function – Component Based Development: Implementation Function Make a formal difference between maintaining the ‘standard’ components and the implemented components. For updates the standard components are leading!
CBSE Analysis Construction Dissemination Domain Engineering Software Architecture Development Domain Analysis t nen mpo ry Co bra Li Domain Model Re. Usable Component Development Repository Re. Usable Components Structural Model Component Based Development Component Qualification ent pon tation m Co men le Imp Analysis Architecture Design Component Update Component Adaptation Component Engineering Application Software Component Composition Testing 16
Domain Engineering • identify, construct, catalog and disseminate a set of software components • that can be applied to existing and future software for a particular domain • Most important functions: – Analysis, Construction and Dissemination
Domain Engineering Analysis • Define the domain to be investigated • Representative sample of applications in the domain – business rules, best practices • Develop a model for the domain
Domain Engineering Construction • Selection of function or object • Reuse? : – Is the functionality needed for future implementations? – What is the degree of reusability (commonality)? – Is there a duplication of the functions in the domain? – Is the component hardware dependent? – Is the design optimal for future implementations? – Can a non-reusable component be re-parameterized such that it becomes reusable? – Is it useful to decompose or re-parameterize a component for reuse? • construct a structural model
Domain Engineering: Dissemination • Library of components • characterization for possible reuse • looking to various aspects for it Product/Technology - Requirements Stability - Concurrent Software - Memory Constraints - Application Size - User Interface Complexity - Programming Languages - Safety/Reliability - Lifetime Requirements - Product Quality - Product Reliability Process - Process Model - Process Conformance - Project Environment - Schedule Constraints - Budget Constraints - Productivity People - Motivation - Education - Experience/Training - Application domain - Process - Platform - Language - Development Team - Productivity
Component Based Development • Analysis of the particular application – referring to the domain model • Architectural design – referring to the structural model • Component qualification, adaption, composition – possible engineer another component • testing
Component qualification • • • can a selected component effectively be reused? its interface development and integration tools required runtime requirements : resources, speed, network protocol services requirements like OS interfaces and support of other components • security features like access control and authentication protocols
Component adaption • Assure that the component integrates easily in the architecture: • consistent methods for resource management for all components; • common activities for e. g. data management for all components; • interfaces between components and the outside world have been developed in a consistent way. • use component wrapping or custom component?
Component composition • assembling of qualified, adapted or engineered components • Common architecture environment, elements: – Data Exchange model: human-to-software, between components, among system resources – Automation, tools macro’s and scripts – Structured Storage, accessing heterogeneous data in a single data structure – Underlying Object Model, assures interoperability
CBSE problems • Component trustworthiness - how can a component with no available source code be trusted? • Component certification - who will certify the quality of components? • Emergent property prediction - how can the emergent properties of component compositions be predicted? • Requirements trade-offs - how do we do trade-off analysis between the features of one component and another?
Ariane launcher failure • In 1996, the 1 st test flight of the Ariane 5 rocket ended in disaster when the launcher went out of control 37 seconds after take off. • The problem was due to a reused component from a previous version of the launcher (the Inertial Navigation System) that failed because assumptions made when that component was developed did not hold for Ariane 5. • The functionality that failed in this component was not required in Ariane 5.
Standard packages • SAP, Oracle, Peoplesoft, etc. • developed for specific business processes; • Strong development in the last years (shift from custom made to standard packages); • ‘Enabler’ of working in a process way (BPR); • ‘Best practice’ business processes build in; • Started in the ERP environment (‘Enterprise Resource Planning’) = primary business processes, extended to many other environments • large changes in methodology for implementation of software systems.
Final remarks • CBSE and standard packages change an implementation from ‘programming to composing’ and from ‘design to select’; • Integration of modules in existing architectures becomes more and more important: interfaces; • Custom made around the standard applications cq. modules becomes complex and has to be integrated; • Aspects with relation to what is leading, my ‘requirement’ or the ‘package’ become important issues; • Management and ‘human factors’ stay the most important aspects for the success of a implementation.