Structured Systems Analysis and Design Methodology

Contains 5 modules:

• • • • •

Feasibility Study (Stage 0) Requirements Analysis (Stages 1 and 2) Requirements Specification (Stage 3) Logical System Specification (Stages 4 and 5) Physical Design (Stage 6)

Methodology: a definition

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A Methodology is a collection of procedures, techniques, tools and documentation which will help the systems developer to develop an information system.

SSADM Version 4

Stages of SSADM v4 annotated to show main uses of the three basic diagrammatic techniques. Notice how the diagrams carry forward from stage to stage becoming transformed from the existing physical system through a logical system and eventually to the required system.

Key to abbreviations: c.p. = current physical diagram c.l. = current logical diagram r.s. = required system diagram DFD = dataflow diagram E.P.D. = elementary process description LDM = logical data model ELH = entity life history

SSADM Version 4

Stage 0: Feasibility Step 010 Prepare for feasibility study

overview LDS context diagram current physical level 1 DFD

Step 020 Define the problem

uses c.p.DFD and overview LDS

Step 030 Select feasibility options

subsets of DFD and LDS used for BSOs and TOs and for estimation of system size and complexity

Step 040 Assemble feasibility report

LDS included in environment descriptions

RJP/SSADM 0/PP

SSADM Version 4

Stage 1: Investigation of the current environment Step 110 Establish analysis framework

level 1 current physical DFD (c.p. DFD) overview LDS

Step 120 Investigate and define requirements Step 130 Investigate the current processing Step 140 Investigate current data

refine & validate LDM in step 130 the c.p.

DFD is updated from results of Step 120

Step 150 Derive logical view of current services

c.p. DFD converted to current logical DFD (c.l. DFD) amend LDM to support c.l. DFD and EPDs as required

Step 160 Assemble investigation results RJP/SSADM 1/PP

SSADM Version 4

Stage 2: Business System Options Step 210 Define business system options Step 220 Select business system options

DFDs and LDM may be used to support both these steps

RJP/SSADM 2/PP

SSADM Version 4

Stage 3: Definition of Requirements Step 310 Define required system processing

amend c l DFD to agree with BSO and LDS (this gives required system DFD)

Step 330 Derive system functions Step 320 Develop required data model

required system LDM prepared use r.s. DFD to identify update & enquiry functions refer to r.s. LDM as necessary

Step 350 Develop specification prototypes

use r.s. DFD and LDM for reference

Step 360 Develop processing specification Step 370 Confirm system objectives Step 340 Enhance required data model

validate and enhance LDM from RDA use r.s. DFD and LDM as inputs to entity/event modelling, creating ELHs, EAPs and ECDs update required system LDM as necessary

Step 380 Assemble requirements specification

cross check LDM against all other products

RJP/SSADM 3/PP

SSADM Version 4

Stage 4: Technical Options Step 410 Define technical system options

LDM now part of requirements spec. which is input to this stage

Step 420 Select technical system options RJP/SSADM 4/PP

SSADM Version 4

Stage 5: Logical Design Step 510 Define user dialogues

requirements spec. input to this stage

Step 520 Define update processes

update entity descriptions in LDM, include state indicators on ELHs and create update process models

Step 530 Define enquiry processes

create enquiry process models

Step 540 Assemble logical design

check LDM and other logical design products for consistency

RJP/SSADM 5/PP

SSADM Version 4

Stage 6: Physical Design

LDM is main input

Step 620 Create physical data design Step 610 Prepare for physical design

LDM is used for reference

Step 640 Optimise physical data design Step 650 Complete function specification Step 660 Consolidate process data interface Step 630 Create function component implementation map Step 670 Assemble physical design RJP/SSADM 6/PP

So…… Questions on the above structure:

1.

2.

How many times in a project are the following diagrams worked on?

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DFD

– –

LDM (what is the LDM?) ELH What are the main artefacts output from each stage?

– – – – – – –

Stage 0 Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6

/Continued………..

And…… Questions on the above structure (continued):

3.

4.

5.

On which life cycle is SSADM based?

•

What is meant by the following: Logical Design

•

Physical Design What does ‘Conceptual Model’ mean?

6.

7.

8.

9.

When is the code written?

When is the system tested?

When is the client/user trained to use the system?

Why is it advantageous to draw models?

10. What are the reasons for having all these three models: the Data Model (inc ERD/LDM), the Process Model (inc DFDs and process specifications) and the Behavioural Model (ELHs)?

11. Where and how does the Project Management happen?

12. Where and how does Quality Assurance happen?