Finishing up on Methods

(or the last bit of JSD and the other methods in brief)

2

JSD Implementation

• In essence we must transform the concurrent specification we have developed into a sequential one.

• Then we start coding.

• We do the transformation by means of process inversion.

3

Process Inversion• Replace data stream connections by

CALL & RETURN instructions• Hence:

• Becomes:

• Then we write a SCHEDULER process

A B

A

B

4

Now read the notes

• Of course, there’s more to it than that, but you can read the book/notes for the details

• yada yada yada

• blah blah blah

• Yoda, Yoda, Yoda, Jedi, Jedi, Jedi...

More Methods

YSM, STRADIS, SSADM, Information Engineering

6

Yourdon Systems Method

• Read the books for details, but essentially:

• A functional decomposition approach

• Though it claims to be “middle out”.

• Uses DFDs, STDs, etc.

7

YSM Features

• Based around a set of models which abstract the main features of what is under examination and then present those features in a useable way

• Enterprise Model

• System Essential Model

8

Enterprise & System

• An enterprise is an economic unit that is resourced and managed as a unit

• A system is a collection of information and operations that are organised to meet a specific problem. – Enterprise is not a system. Has a longer

life-span than a system. Within an enterprise, several systems may be developed, used and replaced.

9

Viewpoints of a System

• YSM takes 3 orthogonal viewpoints:– Function: what the system does. DFDs

are used here.– Time: what happens and when (Use an

Event List that shows what happens to which system must respond).

– Information: what information is used by the system. (use ER models for this)

10

STRADIS

• Gane & Sarson worked with Yourdon in early years hence there is some similarity between these methods.

• Concerned mainly with systems analysis, to a lesser extent with systems design and hardly at all with implementation.

• Uses Functional Decomposition

11

Method Stages

• The initial study

• The detailed study

• Defining and designing alternative solutions

• Physical design

• What do we notice about steps 1-3?

12

Rationale

• Wide applicability in the area of information systems

• Most relevant to a situation in which there is a backlog of systems waiting to be developed and insufficient resources to devote to all potential new systems

• Incorporates a wide variety of established techniques

13

Information Engineering

• Based on work of Finkelstein and James Martin Associates

• A BIG method

• Tends to be used by large organisations for strategic IS development projects

14

Rationale

• Main problem is viewed as the provision of information, not the construction of software

• The basis of the I.S. is data because this is more stable than processes or procedures

• The most appropriate means of communication is through diagrams

15

Stages

• The method has LOTS of stages and steps

• Not all projects will require all stages

• Uses functional decomposition, but with a twist

16

SSADM

• Good grief, what can we say?• H.M. Government standard since 1983• Straightforward F.D. method• Does not address implementation• Version 4 uses FPA• Drone, drone, drone, drone..• Droid, droid, droid, C3PO...

17

Methods X,Y & Z

• And there are many others besides.

• So, what do we do with it all?

• Watch this space...