Eliminating redundancy in specifications.

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Eliminating redundancy in specifications

REDUNDANCY ELIMINATION

Redundancy can be eliminated by systematically applying four identities of Boolean Algebra

These identities are

KARNAUGH MAP REDUCTION

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REDUCING DECISION TABLES-USE OF K-MAP

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Boxes marked X correspond to impossible rules.

They can be employed if they are useful in reducing rules

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REDUCING DECISION TABLES

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EXAMPLE-REDUCTION OF RULES IN WORD STATEMENT

 

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Decision trees for specifications

Reduced rules : Insure if married or male over 30 Obser to 2 and 1 condition removed

Decision Trees is used when sequence of testing condition is important. It is more procedural compared to Decision tables.

EXAMPLE – DECISION TREE TO BOOK TRAIN TICKET

Book by II AC on 4/8/04 if available else book by II AC on 5/8/04.If both not available book by sleeper on 4/8/04 if available else book on 5/8/04 by sleeper. If none available return.

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C1: Is II AC ticket available on 4/8/04

C2: Is II AC ticket available on 5/8/04

C3: Is sleeper available on 4/8/04

C4: Is sleeper available on 5/8/04

Observe in the tree sequencing of conditions which is important in this example

CONDITIONS

• Decision trees are drawn left to right

• Circles used for conditions

• Conditions labelled and annotation below tree

• Conditions need not be binary For example:

For example:

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•Sometimes Decision trees are more appropriate to explain to a user how decisions are taken

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WHEN TO USE STRUCTURED ENGLISH,DECISION TABLES AND DECISION TREES

Use Structured English if there are many loops and actions are complex

Use Decision tables when there are a large number of conditions to check and logic is complex

Use Decision trees when sequencing of conditions is important and if there are not many conditions to be tested

REFERENCES

1. V.Rajaraman, “Analysis and Design of Information Systems”, 2nd Edition, Prentice Hall of India, New Delhi, 2002. Most of the material in this module is based on Chapter 8 and 9 of the above book. The book is perhaps the only one which has extensive discussion on error detection in Decision Tables.

2. K.E. Kendall and J.E.Kendall, “Systems Analysis and Design”, 5th Edition, Pearson Education Asia, Delhi, 2003. Has a brief discussion of structured English, Decision Tables and Decision Trees (pages 353 to 369). Website www.prenhall.com/kendall has a lot of support material and case study for students.

3. J.A.Hoffer, J.F.George, J.S.Velacich, “Modern Systems Analysis and Design”, Third Edition, Pearson Education Asia, 2002. Chapter 7 (pages 282 to 303) cover the topics in this module. The book has a number of interesting case studies and a good problem set. The web site http://prenhall.com/hoffer has material to assist students who use this text book.

4. E.Yourdon “Modern Structured Analysis”, Prentice Hall of India, 1996. Chapter 11 (pages 203 to 232) describes structured English and Decision Tables. There is a larger set of exercises at the end of the chapter.

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