UHD-CMS-CH10 1

Specification Phase

Chapter Ten

UHD-CMS-CH10 2

SPECIFICATION DOCUMENTThe specification document must be• Informal enough for client• Formal enough for developers• Free of omissions, contradictions, ambiguities

UHD-CMS-CH10 3

SPECIFICATION DOCUMENTConstraints

– Cost– Time– Portability– Reliability– Response time

Acceptance Criteria– Vital to spell out series of tests– Product passes tests, deemed to satisfy specs.– Some are restatements of constraints

UHD-CMS-CH10 4

SOLUTION STRATEGY• General approach to building the product• Find strategies without worrying about

constraints• Modify/select strategies in light of constraints• Keep written record of all discarded strategies

and why discarded:– To protect spec team– To prevent unwise new solutions during

maintenance phase

UHD-CMS-CH10 5

SPECIFICATION METHODS• Informal• Semi-formal• formal

UHD-CMS-CH10 6

INFORMAL SPECIFICATIONSExample:“if sales of current month are below target sales,

then report is to be printed, unless difference between target sales and actual sales is less than half of difference between target sales and actual sales in previous month, or if difference between target sales and actual sales for the current month is under 5%”

UHD-CMS-CH10 7

INFORMAL SPECIFICATIONS• Based on Natural Languages• Can be ambiguousClaim:

– ambiguity can not arise when specs done by professionals

Refutation:– Text Processing case (see textbook)

UHD-CMS-CH10 8

INFORMAL SPECIFICATIONS• Conclusion: Natural Language NOT good way

to specify productFact:

– Many organizations still use natural language, especially for commercial products

Reasons:– Uninformed management– Under-trained computer professionals– Management gives in to client pressure– Management unwilling to invest in training

UHD-CMS-CH10 9

STRUCTURED SYSTEMS ANALYSISThree popular graphical specification methods

– DeMarco– Gane and Sarsen– Yourdon

• Equivalent• Equally good• Many US corporations use them for commercial

products• Gane and Sarsen used for Object-Oriented design

UHD-CMS-CH10 10

SSA: CASE STUDY• Sally’s Software Store buys software from

various suppliers and sells it to the public. Popular software packages are kept in stock, but the rest must be ordered as required. Institution and corporations are given credit facilities, as are some individuals. Sally’s store is doing well, but despite her business success Sally has been advised to computerize. Should she?

• Better question: what part?

UHD-CMS-CH10 11

CASE STUDYFundamental issue

– What is Sally’s objective in computerizing her business?

Assume– Objective is “to make more money”

• Cost/benefit analysis for each section of business.

UHD-CMS-CH10 12

CASE STUDYGane and Sarsen Technique:• A nine step method• Stepwise refinement in many steps

UHD-CMS-CH10 13

CASE STUDY• Data flow diagram (DFD) shows logical data

flow (what happens, not how it happens)

UHD-CMS-CH10 14

STEP 1: DRAW THE DFDFirst refinement

UHD-CMS-CH10 15

STEP 1- Second Refinement

UHD-CMS-CH10 16

STEP 1- Portion of third refinement

UHD-CMS-CH10 17

STEP 1 contdFinal DFD

– Larger, BUT easily understood by client

Larger DFDs– Hierarchy of DFDs– Each box becomes DFD at a lower level

UHD-CMS-CH10 18

STEP 2: Decide what parts to computerize

• cost/benefit analysis

STEP 3: Refine data flow• Data items for each data flow• Refine each flow stepwise

order:order identificationscustomer detailspackage details

• Refine further• Need data dictionary

UHD-CMS-CH10 19

STEP4: Refine Logic of ProcessesExample: • Process: Give educational discount

– Sally must explain discount for educational institutions

– 10% on up to 4 packages, 15% on 5 or more• Translate into decision tree

UHD-CMS-CH10 20

STEP 5: Refine Data Stores• Define contents and representation (format)• Specify where immediate access is required

– define type of queries– define Data Immediate Access Diagram (DIAD)

UHD-CMS-CH10 21

STEP 6: Define Physical ResourcesFor each file, specify

– File name– Organization– Storage medium– Records (to field level)

DBMS:– define each table

STEP 7: Determine I/O Specs• Specify input forms, input screens, printed output

UHD-CMS-CH10 22

STEP 8: Perform SizingDetermine data for step 9:

– Volume of input (daily or hourly)– Size, frequency. Deadline for each printer report– Size, number of records processed– Size of each file

UHD-CMS-CH10 23

STEP 9: Hardware Requirements– Mass Storage requirements– Input needs– Output devices– Is existing hardware adequate?

However– Response time can NOT be determined

UHD-CMS-CH10 24

ENTITY-RELATIONSHIP DIAGRAMS• Semi-Formal technique• Data-Oriented • Widely used in specifying databases• used for Object-Oriented Analysis

• Example: Author, Biography, Reader

UHD-CMS-CH10 25

ENTITY-RELATIONSHIP DIAGRAMS

1-to-many relationships

UHD-CMS-CH10 26

ENTITY-RELATIONSHIP DIAGRAMS

Many-to-many relationships

UHD-CMS-CH10 27

FORMAL TECHNIQUES• Finite State Machines• Petri Nets• Z

UHD-CMS-CH10 28

FINITE STATE MACHINES• A safe has a combination lock that can be in one of

three positions labeled 1, 2 and 3. The dial can be turned left or right (L or R). Thus there are 6 possible dial movements: 1L, 1R, 2L, 2R, 3L, and 3R. The combination to the safe is 1L, 3R, 2L. Any other dial movement cause the alarm to go off.

UHD-CMS-CH10 29

FINITE STATE MACHINES• Set of states: (SafeLocked, A, B, SafeUnlocked,

SoundAlarm)• Set of inputs:( 1L, 1R, 2L, 2R, 3L, 3R)• Transition function:• Initial State: SafeLocked• Set if final states: (SafeUnlocked, SoundAlarm)

UHD-CMS-CH10 30

FSM--State Transition Diagram(STD)

UHD-CMS-CH10 31

FSM--State Transition Table

UHD-CMS-CH10 32

EXTENDED FSM• Extended FSM with global predicates

– predicate: condition in terms of global state/event or a combination of them

• Transition rules have form:– State and Event and Predicate ==> New State

UHD-CMS-CH10 33

ELEVATOR PROBLEM

UHD-CMS-CH10 34

ELEVATOR PROBLEM

UHD-CMS-CH10 35

ELEVATOR PROBLEM

UHD-CMS-CH10 36

ELEVATOR PROBLEM

UHD-CMS-CH10 37

ELEVATOR PROBLEM

UHD-CMS-CH10 38

ELEVATOR PROBLEM

UHD-CMS-CH10 39

ELEVATOR PROBLEM

UHD-CMS-CH10 40

UHD-CMS-CH10 41

POWER OF FSM TO SPEC COMPLEX SYSTEMS• Specs take simple form• Specification is

– Easy to write down– Easy to validate– Easy to convert into design– Easy to generate code automatically– More precise than graphical methods– Almost as easy to understand

• However– Timing considerations not handled

UHD-CMS-CH10 42

WHO IS USING FSMS?• Commercial Products

– Menu driven– Various states/screens– Automatic code generation a major plus

• System Software– Operating systems– Word processors– Spreadsheets

• CASE tools– Statemate

UHD-CMS-CH10 43

PETRI NETS• Powerful technique for specifying systems with

potential timing problems– Concurrency and synchronization– Race conditions– Deadlock– originally used by automata theorists– now used in performance evaluation, O/S, and SE

fields

UHD-CMS-CH10 44

Formal Specifications - Cont.• Z

– a formal specification language– uses set theory, functions, and discrete math.– Initially difficult to learn– the most widely language

UHD-CMS-CH10 45

Testing during Spec. Phase• Walkthrough• Inspection (more powerful)

– team of inspectors checks specs against a checklist

• If a formal tech. is used other testing tech. such as correctness-proving methods can be applied, simulation of FSM/Petri Nets etc.

UHD-CMS-CH10 46

CASE tools• Two classes

– Graphical tools• DFD, FSMs, Petri nets, ER diagrams

– Data dictionary• the two should be integrated• E.g.,

– Analyst/Designer, Excelerator, software through pictures, system architect, and Teamwork

UHD-CMS-CH10 47

Metrics• Five fundamental metrics

– size• number of items in the data dictionary

– cost– duration– effort – quality

• number faults found during inspection• This information is tentative at best