Software Engineering

Lecture 21: Component-Based Software Engineering

Today’s Topics Issues and Challenges for CBSE The CBSE Process Guidelines for Reuse The Reuse Environment Economics of CBSE Metrics for CBSE

Characteristics of CBSE Analysis & Design includes checking for

reusable solutions A “more organized approach” to software reuse Helps reduce development time & cost (with

streamlined infrastructure & process) Less emphasis on implementation, more on

integration

Challenges for CBSE Does the domain allow reusability?

Systems have common requirements Can the extra cost be justified?

High degree of reusability Can support for reuse be created?

Indexing, common access, process Can incentives be created for engineers?

Appropriate culture, metrics, etc.

Composition Follows architectural design & precedes detailed

design Can requirements be implemented:

• By COTS components?• By internally-developed components?

Are component interfaces with the architecture compatible?

Can the requirements be adjusted to accommodate reuse?

CBSE Activities Component Qualification

Does the component fit the need? Component Adaptation

Resolve design mismatches Component Composition

Adopt framework for integration Component Update

Manage third-party updates

Types of Components Run-Time Components

• Dynamic binding• Interface discovered at run-time• E.g.: distributed objects (CORBA)

Business Components• Encapsulate an autonomous business concept or process• E.g.: enterprise Java beans (EJB)

CBSE Development Process Identify, qualify, adapt, assemble, and update

reusable componentsComponent engineering

Domain engineering and component engineeringare concurrentRequirements are adjusted to accommodate reuse

TheCBSEProcess

[From SEPA 5/e]

Domain Analysis Define the domain Categorize the items in the domain Collect a sample of applications Analyze each application Develop and analysis model for the domain

objects

Identification & Categorization Select specific functions or objects Abstract functions or objects Define a taxonomy Identify common features Abstract the relationships Derive a functional model Define a domain language

Example: Common Objects Text processing objects share common functions

• Process sentence & provide feedback• Process sentence & provide an output (rewrite, translation)• Process sentence & provide markup

Text processing programs share common context (desktop)

Example [2] Shared Objects

• Client: a program that resides on the desktop, interfaces with a word-processing program, and provides some functionality on the desktop

• Server: a program that resides remotely and does the actual work

The KANT system (CMU) provides reusable boundary objects which are used in several applications

Other Examples Document class in Java

(also its subclasses) User Interface components

(e.g., Java Swing classes) Database interface components (e.g. reusable

JDBC classes)

Guidelines for Reuse Is there a future need? Is the functionality common? Is the functionality duplicated? Is there a hardware dependency? Is the design optimized? Can we parameterize components? Can we reuse via modification? Can we decompose a component to derive reusable

components?

Domain Characteristics Impact Reusability

[From SEPA 5/e]

Structure Points Capture a repeating pattern in the domain

(function, data, behavior)e.g., aircraft avionics system

Three characteristics:• Limited number of instances• Simple rules, interface• Implements information hiding

Generic Structure Points Application Front End (GUI) Database Computational Engine Reporting Facility Application Editor

Can be used for estimation

Component Qualification Does the component:

• Perform the function required?• Fit into the architectural style?• Have the right qualities?

Things to consider:• API, tool support, run-time requirements, maintenance

requirements, security, design assumptions, exception handling, …

Component Adaptation Ultimate Goal: “easy integration”

• Consistent resource management• Common data management• Consistent interfaces

Alternative: Component Wrapping• White-box (modify code)• Gray-box (extend code / data)• Black-box (pre-/post-processing)

Component Composition Four architectural ingredients:

• Data exchange modele.g., drag/drop, cut/paste

• Automationtools, macros, scripts

• Structured storagesingle interface to heterogeneous data

• Underlying object modelensure component interoperability

Integrated Information Management•Flow-based information processing architecture•Shared object model (Node, Document, etc.)•User-defined nodes & resources•Rapid development of reusable components

Emerging Standards OMG/CORBA

Common Object Request Broker Architecture Microsoft COM

Component Object Model Sun Java Beans

Enterprise Java Beans –well-suited for eCommerce

Classification & Retrieval 3C Model [Tracz 1990]

• Concept: What does it do?• Content: How is it built?• Context: What is the domain?

Indexing Schemes• Controlled vocabulary• Uncontrolled vocabulary

ClassificationHierarchy

[From SEPA 5/e]

The Reuse Environment Component Database Library Management System Component Retrieval System CBSE Tools for Integration

Example of a web-based component library: www.jars.com

Economics of CBSE Quality

Lower defect rate for reusable code Productivity

Faster delivery of complete systems Cost

Savings = CS – (CR + CD)

Develop from Scratch Cost of Reuse Develop w/Reuse

Reuse Metrics Reuse Benefit (cost-based)

Rb(S) = [Cnoreuse – Creuse]/Cnoreuse

Reuse Leverage (object-based)Rlev = OBJreused / OBJbuilt

Questions?