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...