STRUCTURED SYSTEMS ANALYSIS PART ONE

CM00308 - 1Systems Development Tools Techniques &

Methods

What we will cover Slide 2 of 20

ApologiesSystem modelling generallyWhat is a model?Why model a systemA summary of modelling approaches

System modelling generally Slide 3 of 20

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a miracle happens!

And lo …

What is a model? Slide 4 of 20

That was a model!An abstracted representation of something

that enables the identification of relevant elements, components and their inter-relationships

For example: An OS map of North Staffordshire A YHA map of North Staffordshire A cycling map of North Staffordshire A road map of North Staffordshire

All show the same territory, but …

Why model a system? Slide 5 of 20

to find out what is and/or what should be going on

to allow system developers to understand and communicate with system users/sponsors

to provide a framework that handles complexity, allowing decomposition

it’s cheaper to model than to buildenables “look ahead”

Why model a system? - summary

Slide 6 of 20

Enables you to “go there” in your head before you write any code things can be identified and sorted into the

important and the not-so-important problems can be identified (and possibly even

solved) early clarifies woolly ideas allows issues to be raised and discussed early facilitates more sensible decisions helps you to find out what you don’t know saves embarrassment later

Modelling/development approaches

Slide 7 of 20

Object oriented approachesStructured approachesCollaborative approaches

RAD, Prototyping, DSDM …….

Agile approaches SCRUM, XP etc Today’s challenge – what does SCRUM stand for? prizes next time

Other approaches

Structured modelling

Separates the consideration of: what a system does (or is to do) from the data and the (relational) data structures that are

required to enable it to do itIs all Edgar Codd’s fault (from 1970) Process modelling - covers the whatData modelling - covers the structure of the

data needed to support what is happeningTime and Event modelling – cover things that

Process Modelling doesn’t do very wellStructured modelling includes some useful

techniques that are generically applicable Slide 8 of 20

Process Modelling Slide 9 of 20

does what it says on the tin!for any information system, models

processes (at various levels of detail) participants data required/processed/stored/transmitted

pictures give framework for detailed descriptions

Data Modelling Slide

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Models the data required to enable a system to perform it’s defined functions (processes)

and how this data should be structured when persisting

Loads more of this later in the moduleThis is an area which improved greatly

with practice and, at first, seems incomprehensible and impossible

Useful structured modelling tools and techniques Slide

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Included here as they do not really fit neatly into the process and/or data categories Aim of a system Levelling Problem/Requirements lists Data dictionary

But, Process and Data modelling are implicitly included!

Aim of a system Slide

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a (short) paragraph to define succinctly what a system does (and does not) do

For a company’s retail system “To support the correct administration and accounting

of ordering, packaging and sales of goods through its shop and mail order operations”

Aim of a system - examples Slide

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A payroll system “To enable the correct calculation of gross pay and

deductions for all weekly paid employees. Funds will be transferred electronically.”

A lift system “To transport a maximum of eight people between

floors in a safe and timely manner”

Levelling Slide

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Incredibly useful for those of us bears with very little brain

Found in SAD structured process modelling but generically applied often

Handles complexity through grouping of low level functions and/or by decomposing high level functions

Each level lower has more detail than higher level(s)

Links high and low level functions allowing simultaneous consideration of all levels

Levelling - graphically

Slide 15 of 20

Somethingcomplex

Somethingless complex

Somethingless complex

Somethingless complex

Somethingless complex

Somethingeven simpler

Somethingeven simpler

Somethingeven simpler

Somethingeven simpler

Somethingsimpler

Somethingsimpler

Somethingsimpler

Somethingsimpler

Problem/Requirements list Slide

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A numbered list of all the problems with the current system and (usually hence) requirements of a new system

Does not differentiate between whether issue is a problem or a requirement

Includes the sublime, the ridiculous and all points between

Serves as a check-list when conceiving and designing new system

Helps to prevent problems and requirements becoming lost in the maw (mire) of analysis and design methods

A word or two about your assignment Slide

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StartIt!

What we have covered Slide

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System modelling generallyConsideration of a model and what it isWhy model a systemIdentification of different modelling

approaches. . . Elements of structured approachesAssignment guidanceWhat comes next

What’s next? Slide

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Process Modelling proper Where and why it fits into Software Development Data Flow Diagrams – what and how More on levelling How it all fits with other structured modelling

techniques

References Slide

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Essentials of Systems Analysis and Design, Valachi, George and Hoffer, Pearson Prentice Hall

Software Engineering, Ian Sommerville, Addison Wesley, 2000

Software System Development – A Gentle Introduction – Briton and Doake, McGraw Hill