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Lesson 1 – Component-Based Software Development Software Engineering Module 1 - Components Teaching unit 3 – Advanced development Ernesto Damiani Free University of Bozen-Bolzano CBSD • CBSD (Component-Based Software Development) also referred to as CBD (Component-Based Development), is the creation and deployment of software intensive systems assembled from components, as well as the development and harvesting of such components Why you should learn SW Component Technologies ? • CBD enables higher level of SW reuse • CBSD is the de facto paradigm for developing large SW systems – enterprise-scale distributed applications – N-tier Web applications Software Industry: Challenges (1) • Constant innovation in hardware and software – Powerful and sophisticated applications to desktops and across networks • Large and complex applications – Time-consuming to develop, difficult and costly to maintain, risky to extend with additional functionality • Monolithic applications – Large number of features, features that cannot be removed, features that are upgraded independently or replaced with alternatives easily Software Industry: Challenges (2) • Not easily integrated applications – The functionality of one application cannot be available to other applications even if they use the same machine and are written in the same language • Not sufficiently modular operating systems – It is difficult to override, upgrade, replace services in a clean and flexible fashion • Not consistent programming models – It depends upon where the service comes from: same address space as the client, separate address space on the same machine, from the operating system or from a provider running on a separate machine across the network Barriers to Integration • End user: wealth of end user applications, tools • Enterprise investment: wealth of enterprise vital services Aim is Barrier Free SW Reuse • “To be able to use whatever from wherever” Attempts at Software Reuse • Source code copy and reuse – Poorest form of reuse • Procedural function libraries – Better form of reuse, than source code copy – Not extensible • Class libraries – Still better form of reuse; extensible – Necessary a lot of understanding before classes can be reused – Support white-box reuse; clients affected if internals of classes changed – Language specific; no reuse across code in other languages – Incompatible with other compilers/linkers other than that used in the development of the library Software Reuse Strategies (1) • White-box reuse – Source of a sw component is made available and can be studied, reused, adapted or modified. – OO frameworks provide this form of reuse rely on inheritance for reusing SW implementations • Drawback: clients depend on the internals of a component and will be adversely affected if the internals change Software Reuse Strategies (2) • Black-box reuse – Based on the principle of information hiding – Interfaces specify the services a client may request from a component; components provide implementations of interfaces – Interfaces specify only descriptions of component behavior (operation signatures); do not include any implementation – Clients rely only on interfaces; component implementations of the interfaces are totally hidden from the clients – Advantages: as long as the interfaces remain unchanged, components can be changed internally without affecting clients SW Component Technology • SW components provide mechanisms for a greater level of SW reuse. They support black-box software reuse. What is a SW Component ? • A package of software that provides some coherent functionality, can be independently developed and delivered as a unit, and provides its services through well-defined interfaces – modular implementations of significant business or system functionality – adheres to a component model Component-Based SW Development • Developing of applications by assembling SW components • Shifting of the emphasis from programming SW to composing SW systems Component-A Component-B Component-C Component-D CBSD – Programming Model • Interface-based Programming • Clients program to interfaces – Clients do not need any knowledge of how a component implements its interfaces – as long as interfaces remain unchanged, clients are not affected by changes in interface implementations Interfaces A Client program B <<realize>> <<realize>> Component-1 … <<realize>> Component-2 Example Getfinalgrade(set of marks, Grade) IComputeGrade Marks Calculator Student Marks Report program IBarChart drawChart(set of data) Bar Chart IDataAccess connectToDB(connection params) Getmarks(student-id, marks-list) Database component FINE