Requirements Models to Architectural Design Models: A

Simple Library Example

Robert France

Colorado State University

What is architectural design?

• Concerned with identifying subsystems and their relationships

• Architectural design is an example of programming-in-the-large– Basic element of construction is a subsystem or

layer or system component (unlike programming-in-the-small where the basic unit of construction is a statement in a programming language)

• Subsystems are systematically refined to show more details in detailed design.

Architecture Types• Logical Architecture

– Organization of a system into logical units (e.g., layers, subsystems)

– Logical units do not necessarily result in units of implementation (e.g., Java packages, components)

• Implementation (Deployment) Architecture– Organization of a system into physical units

(e.g., source files, Java packages, components)

Layered Architectures

• Separate presentation and application logic, and other areas of concern.

UI Layer

“Domain” or “Application Logic” Layer

Services Layer

PersistenceSubsystem

LoggingSubsystem

. . .

Component Architectures

• An architectural component is an architectural unit provides a well defined set of services.

• An architecture is constructed by composing components.

• A component has two types of interfaces– Provided interface: describes the services provided by

a component– Required interface: describes the services that the

component requires to provide its services

Transitioning to Architectural Design

Requirements class model

Requirements use case

Architectural static model

Architectural sequence models

Identify subsystems by grouping use cases

Identify subsystems by grouping classes

Describe how subsystems interact to accomplish use cases

Simple Library Example

• Library consists of reference and general copies– Only general copies can be chacked out;

reference copies cannot be checked out

• A borrower cannot check out a copy if they have outstanding fines.

• A borrower is charged $1 for each week after its due date that it is not returned.

Library Example: required services

CheckOutCopy

ReturnCopy

AddCopy

DeleteCopy

AddBorrower

DeleteBorrower

FindCopy

CheckOutCopy UseCase (draft form)

UseCase: CheckOutCopy

Main flow

1. Clerk enters borrower and copy identifiers

2. If borrower is registered, does not have fines, and copy is a general copy then system indicates that checkout is successful; else system indicates that checkout is not successful

Requirements Class Model

Architectural Static Model

Use cases grouped into borrower services and administrative services; two subsystems for each of these groupings is created – one responsible for borrower services, the other for administrative services Both administrative and

borrower services need copy and borrower information. This observation results in a decision to include two subsystems for managing copies and borrowers.

CheckOut Sequence Model

ReturnCopy Sequence Model