SSA(D) vs OOAD M. Pickard CSC 513

Different Perspectives . . . SSA (and design) Data and actions considered separately. Emphasis on data structures, procedures. OOAD Data and actions considered together. Emphasis on classes, objects.

Steps in OOA Use-case modeling Class Modeling Dynamic Modeling

OOD Create interaction diagrams sequence diagrams, collaboration diagrams Build a detailed class diagram, or object model packages of classes relationships owned by the package hierarchy of packages Design the product using objects Proceed to detailed design

Structured Systems Analysis (SSA) Analysis, resulting in Specifications 9 Step Approach (Gane and Sarsen) Draw DFD Define scope of product & operational approach Refine/define data flows Define logic of processes Define data stores Define physical resources Determine I/O specifications Perform sizing (volumes, frequencies) Determine hardwire requirementss Other variations

SSA - Specifications Semiformal techniques Data Flow Diagram (DFD) Entity Relationship Diagram (ERD) Decision (Logic) Table (DLT) Decision Tree

SSA - Specifications Formal techniques Finite State Machines Petri Nets Z Formal specification language pronounced “zed” Other

Structured Methods - Design Architectural design Structure charts Map DFDs to structure chart Global data structures Proceed to detailed design

SSA(D) vs OOAD The differences become very apparent in the activities that take place after requirements gathering and before detailed design. SSAD does not preclude use of OOPL. OOAD does not preclude use of procedural language.

Architectural Design - Important Principles Minimize coupling Maximize cohesion Use information hiding Documentation design decisions design architecture

Detailed Design Identification of modules, i.e, program unit purpose, preconditions, postconditions Description of interfaces between program units Module specifications narrative or structured English semiformal or formal methods to describe module functionality DLT, FSM, other linked closely to implementation environment programming language, operating system, etc definition of local data structures

Implementation Using the detailed design, construction begins . . .