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

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

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

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.

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

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.

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)

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

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

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

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.

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

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:

Function Navigation Models Web Browse and Buy Place Order Make Payment

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

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

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

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