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Structured Systems Analysis and Design Methodology

Structured Systems Analysis and Design Methodology. Northern College Diploma Philip Bird. Why Bother?. Need to plan and organise – link to life cycle. Help communicate ideas. Get processes (functions) right – Data flow modelling. Get data right – Entity modelling.

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Structured Systems Analysis and Design Methodology

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  1. Structured Systems Analysis and Design Methodology Northern College Diploma Philip Bird

  2. Why Bother? • Need to plan and organise – link to life cycle. • Help communicate ideas. • Get processes (functions) right – Data flow modelling. • Get data right – Entity modelling. • Cross reference the two – checks built-in. • Can be automated.

  3. Data Flow Modelling • Describe the current physical system. • Show processes together with data flows between them. • Show data stores. • Use these to discuss problems with users and help identify requirements for new system.

  4. Check stock availability Copy order Customer Order Stock level Product Order Order Order

  5. Entity Modelling • Things the system needs to store data about • Physical – cars, products • People – customers, employees • Abstractions – order, invoice, booking • Each entity has a unique identifier – key attribute/field. • Entities linked via relationships.

  6. One to One 1:1 Woman Is the husband of Is married to Man

  7. One to Many 1:N Tutor Has Is allocated to Student

  8. Actor Has Role Appears in Film Many to Many M:N Actor Film

  9. Entity Attributes ° Employee number Name Address Tax code NI number Pay to date Tax to date Employee °Key field

  10. An Example – Hire Car Booking Customer Customer#, Name, Address, Tel Booking Customer#, Date, Car reg, Duration Car Car reg, Make, Model, Type, Seats, Cost Date, Mileage, Description, Mechanic Service Name, Qualifications Mechanic

  11. Entity Life Histories • Describes the entity over time. • Check to see there are no missing processes. Are there processes to create, update and delete the entity? • Produce diagram that serves as an initial program design.

  12. ELH For Appointment Entity Appt Make Appt Change Appt * Visit New Year Where in the DFD is there a process to change an appointment? º º º = Alternative Has Appt No Appt * = Repetition

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