1. October 2004J. B. Wordsworth J4ISDSPE1 Information Systems Development Specification

2. October 2004J. B. Wordsworth J4ISDSPE2 Objectives Describe the structure of a specification document for the API process. Understand the role of sets, state, invariant, initialisation, and functional interface in the specification of an API. Understand what is meant by validating an initialisation. Describe the format and significance of the parts of the abstract specification of an operation. Use pseudocode to explain the use of an API for solving application problems. Use a use case definition to validate a pseudocode implementation of a use case.

3. October 2004J. B. Wordsworth J4ISDSPE3 Specification document Specification of the API –Specify the sets, state, invariant, and initialisation. –Validate the initialisation. –Specify the functions of the API. Syntax, inputs, precondition, postcondition, outputs –Validate the functions. Justification of the API –Use pseudocode to illustrate the use cases. –Validate the pseudocode by comparing it with the use case specifications.

4. October 2004J. B. Wordsworth J4ISDSPE4 Abstract specifications Precise definition of state and function Verification and validation opportunities Not biased towards any implementation

5. October 2004J. B. Wordsworth J4ISDSPE5 Sets Identify the different types of information: –Checkout numbers –Line numbers –Prices –Descriptions –Stock levels Used to build up a data model of the state.

6. October 2004J. B. Wordsworth J4ISDSPE6 State Subsets –checkout_set –line_set Functions –price_function –stock_function –description_function –bill_line_function Relations Sequences Numbers Strings

7. October 2004J. B. Wordsworth J4ISDSPE7 CheckoutNumberSequence of LineNumber c1 c2 c3 c4 c5 c6 c7 c8 checkout_set

8. October 2004J. B. Wordsworth J4ISDSPE8 n1 n2 line_set LineNumber Integer 59 1998 20 -5 0 Description d5 d6 d7 d4 d3 d2 d1

9. October 2004J. B. Wordsworth J4ISDSPE9 Invariants (B1) The domain of description_function is line_set. (B2) The domain of price_function is line_set. (B3) The domain of stock_function is line_set. (B4) The domain of bill_line_function is a subset of checkout_set. (B5) The range of every sequence in the range of bill_line_function is a subset of line_set.

10. October 2004J. B. Wordsworth J4ISDSPE10 Initialisation checkout_set is empty. line_set is empty. description_function is empty. price_function is empty. stock_function is empty. bill_line_function is empty.

11. October 2004J. B. Wordsworth J4ISDSPE11 Operations Syntax: –Output-value-list <-- function ( input-value-list ) Precondition –Assumptions about the inputs and the current state Postcondition –partitioned according to situation Validation –Check that the change of state respects the invariants.

12. October 2004J. B. Wordsworth J4ISDSPE12 c1 c2 c3 c4 c5 c6 c7 c1 c2 c3 c4 c5 c6 c7 CheckoutNumber checkout_set CheckoutNumber checkout_set

13. October 2004J. B. Wordsworth J4ISDSPE13 CheckoutNumberSequence of LineNumber c1 c2 c3 c4 c5 c6c7 c8 CheckoutNumberSequence of LineNumber c1 c2 c3 c4 c5 c6c7 c8

14. October 2004J. B. Wordsworth J4ISDSPE14 CheckoutNumberSequence of LineNumber c1 c2 c3 c4 c5 c6c7 c8 CheckoutNumberSequence of LineNumber c1 c2 c3 c4 c5 c6c7 c8

15. October 2004J. B. Wordsworth J4ISDSPE15 A pseudocode function BEGIN status <-- addCheckout (checkout_number) ; IF status = 0 THEN write "Checkout added." ELSE write "Checkout number already in use." END