Function Definition

1. Function Definition • From Investigation to Specification • Defining Functions • The Universal Function Model • Identifying and Documenting Functions • Function Navigation Models • Dialogues

2. Investigation FEASIBILITY Feasibility Report Develop Business Activity Model Requirements Catalogue BAM Overview LDS BAM Overview DFM BAM Investigate Investigate Investigate Current and Define Current Data Requirements Processing Current Physical DFM Task Models Requirements Catalogue Current Environment LDM Derive Logical View of Current Services User Catalogue Logical DFM Current Environment LDM Requirements Catalogue Task Models Assemble Investigation Results

3. Specification Investigation BSO User Catalogue Task Models BSO Define Work BSO Requirements Catalogue Practice Model Requirements Catalogue Current Environment LDM Logical DFM User Catalogue Task Models User Roles Develop Users’ Develop Define Required Conceptual Required Data System Models Model Processing User Object Models Required System DFM Req. System LDM Task Models User Object Model Enhance Derive System Task Models Required Data Functions Requirements Catalogue Model Function Definitions Req. System LDM Function Definitions Develop Develop Processing Specification Specification Function Prototypes Definitions Window Specifications Window Navigation Models Task Models Entity Life Histories Help System Required System LDM Specifications Effect Correspondence Diagrams Requirements Catalogue Enquiry Access Paths Assemble User Object Models Requirements Catalogue Requirements Dialogue Structures Specification

4. Defining Functions The technique of Function Definition serves a number of different purposes: • To define the services that the computerised system will offer its users; • To help analysts and users towards a shared understanding of what the system will do; • To provide the basis for the system’s specification; • To ensure that all design products are traceable to requirements.

5. Defining Functions • The services offered by a computerised information system to its users are known as Functions • The Functions that are available to a given user depend on that user’s role • Functions are usually accessed through a series of one or more menus • Functions usually involve the user in some sort of dialogue with the system

6. Defining Functions For each Function we will have to: • Design the human computer interface (and where applicable interfaces with other computer systems). • Specify the database processing that supports each Function. • Consider ways of preventing erroneous data from ending up in the database. • Gather information that can be used to predict and tune the performance of the Function. • Ensure that the work done on each Function is not duplicated elsewhere and make use of work already done elsewhere. • Ensure that the Function is included in the user’s training manual.

7. Function Definition Concepts • We can define the concept of a Function in several ways, which together give a good idea of what a Function actually is: • A Function is a set of processing that users wish to carry out at the same time • A Function is a set of processing designed to handle the effects of an event (or group of events) on the system • A Function is the basic unit of processing for input to Physical Design (where programs will be specified to implement it)

8. Function Types • Enquiry or Update • User or System Initiated • On-line or off-line We classify each Function in three main ways:

9. Function Components Function Valid Output Output Process Update or Event & Function Input Events Enquiry Enquiry Input Enquiry Process Output Process Triggers Integrity Function Errors Error Syntax Control Error Output Errors Errors Process Database Function Definition Boundary

10. Identifying Functions 1 Maintain Purchase Order D3 Products 1.1 b Product Details Create Proposed Purchase Order Supplier D7 Suppliers P.O.Quantities Purchaser Details Depot Address * D6 Depot 1 Proposed P.O. Purchase Order Availability 1.2 a Confirm Purchase D1 Supplier Amended P.O. Purchase Orders Amended P.O. Order * 2 Delivery Details Delivery Schedule 1.3 i Delivery Arrange Stock Clerk Schedule Delivery 3 *

11. Identifying Functions • Enquiry functions (other than those which form a major part of the systems functionality) will be documented in the Requirements Catalogue, rather than the Required System Data Flow Model. Each enquiry entry in the Requirements Catalogue will initially be identified as a function in its own right.

12. Documenting Functions • An identifier • The Function’s Name • The Function’s type • A description • The business event • The business activity • Error handling • The system event or enquiry • The User Role • DFD Processes For each Function we record • I/O Structures & Descriptions and Dialogues • Requirements • Tasks • User Object Model • Windows • Common Processing • Service Level Requirements • Volumes

13. Function Navigation Models • the Function is very large and it is more manageable to break it down into several parts • the Function contains more that one event/enquiry: we can define one or more components for each event and enquiry • there are parts of the function that will be used by other functions too: again events and enquiries will often feature in more than one function. Functions may be broken down into components when:

14. Function Navigation Models Web Browse and Buy PlaceOrder MakePayment

15. Identifying Dialogues A good way of identifying dialogues is to use the Function Definitions and User Role documentation to identify exactly who will require access to each function. The easiest way of documenting this is by using a User Role/Function Matrix

16. Identifying Dialogues Function User Role Delivery Scheduler Goods In Clerk Purchaser P. O. Clerk Stock Keeper X X X X X X X X X X

17. Critical Dialogues Function User Role X X X Delivery Scheduler X X X Goods In Clerk X Purchaser P. O. Clerk X X Stock Keeper X

18. The Place of Function Definition Investigation BAM RD DFM BSO Specification WPM Conceptual Model External Design LDM User Organisation Policies and Procedures Decision Structure RDA FD Internal design Construction