information process modelling DFDs Process description

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1 Process modelling IMS9300 IS/IM FUNDAMENTALS information process modelling DFDs Process description processes are the action part of businesses process modelling graphically represents the processes which act on data/information to capture manipulate store distribute Process modelling Data Flow Diagrams principal techniques data flow diagrams associated techniques for modelling the details of low-level processes structured English: describing the process in simple phrases decision tables and decision trees: describing the process graphically, especially if the process can have alternative outcomes model the flow of data into, through, and out of an information represent an information as a network of communicating processes show the processes that change or transform data show the movement of data between processes doesn t show exceptions doesn t illustrate sequence 3 4 Components of a DFD Process process data flow data store Membership Fines loan details represents the work performed which changes data transforms incoming data flows into outgoing data flows has a unique number and name source/sink membership 5 6

2 Data Flow Data Store represents data in motion describes a "packet" of data or data that move together may consist of many individual, related elements that move together to the same destination loan details represents a collection of data flows at rest has a unique name which should describe the contents of the data store may represent many different types of physical locations of data may be a temporary or a permanent repository of data Fines 7 8 External Agent External Agent represents an external entity in the environment with which the communicates a source if it is an origin of data coming into the a sink if it is a destination for data leaving the external agents are outside the and define its boundaries what a sink does with data it receives from the and how a source produces data which it inputs to the are outside the boundary of the and are not shown on the data flow diagram eg. Saltwater Shire Administration 9 10 Example Data Flow Diagram member details Members.1 record new member Member Member number, Member name Member. issue Member identification member card purchase order 11 Guidelines for Drawing DFDs each object on a data flow diagram must have a unique name each process must have at least one data flow coming in (input) and at least one data flow going out (output) the inputs to a process are different from the outputs of that process (and so have different names!) a process must be able to build its outputs using only the information in its input data flows plus any constant information 1

3 Guidelines for Drawing DFDs Guidelines for Drawing DFDs data flows are permitted: between processes from a data store to a process from a process to a data store from a source to a process from a process to a sink data flows are NOT permitted: between external agents between data stores from an external agent to a data store 13 see page 87 in Hoffer, George and Valacich 14 Levelling Data Flow Diagrams Context Diagram the entire is represented as a single process any "real" is too large to represent as a single data flow diagram the solution is to decompose the into a hierarchy of levels of processing the process model of the then consists of a set of levelled data flow diagrams all external agents (sources and sinks) are shown no data stores are shown: they are inside the boundary of the SALTWATER LIBRARY Example Context Diagram Level Zero Diagram Sales Order System sales order goods returned purchase order the level zero data flow diagram is the diagram at the level immediately below the context diagram it "expands" the single process on the context diagram to show the major, high-level processes (or functions) within the goods unavailable notice Inventory System supplier delivery 1.0 membership 4.0 levy fines.0 Warehouse shipping slip checked supplier invoice Accounts Department pay bills 3.0 loans 17 18

4 Level Zero Diagram Example Level Zero Diagram all external agents (sources and sinks) are included because the level zero diagram, like the context diagram, represents the entire the number of each process ends in.0 which corresponds to the level of the diagram: e.g. 1.0,.0, 3.0 etc. 19 Order Entry System out of stock notice Warehouse sales order 1.0 Fill Sales Orders shipping slip.0 Monitor Stock levels Stock file purchase order 3.0 Accept Deliveries supplier delivery Accounts checked supplier Department invoice 0 Levelling DFDs DFD Exercise 1 Context diagram 1 Context Diagram Saltwater Library External agents Name the process Identify the data flows that pass over the boundaries of the Level zero diagram 1. Diagram 1 (at Level 1) 1 DFD Exercise 1- Context Diagram DFD Exercise Level Zero Diagram Saltwater Library Data flows from context diagram Analyse the business tasks Identify classes, groups of processes Name the group of processes Analyse processes information required (input), information produced (output) Identify data stores (resting data) 3 4

5 DFD Exercise - Level 0 Diagram Process Description the processing that occurs within processes in DFDs needs to be defined detailed process descriptions form part of the data dictionary: they define the contents of primitive processes many techniques can be used to define the details of processing: e.g. narrative text, Structured English, decision tables, decision trees, flow charts 5 6 Detailed Process Definitions Example Structured English detailed process descriptions should: express what the process does (i.e. policy), not how the process is carried out (i.e. procedure) be in a form that can be easily understood and verified by both users and s analysts be in a form that can be easily communicated to all potential stakeholders e.g. end-users, s analysts, managers, designers, project leaders, programmers Accept sales-order Find customer-details If customer-details not found Then reject sales-order Else Create sales-order-header Do while more sales-order-items find item-details calculate sales-order-item price = item price *order-qty Enddo Authorise sales-order Endif 7 8 Example Decision Table Decision Trees avg account bal > $1,000 overdraft amount < $50,000 previous paid-out loan approve conditional approval reject Y Y Y Y N N N N Y Y N N Y Y N N Y N Y N Y N Y N X X X X X X X X 9 decision trees are an alternative graphical representation of a decision situation as a connected series of nodes and branches wholesale customer retail customer Determine Customer Discount local item imported item local item 1% imported item 15% 10% 7% 30

6 Selecting Techniques for Process Descriptions Process Modelling Techniques Structured English is useful where a process has a sequence of activities and there is no more than three levels of nesting of decisions decision trees and decision tables are useful where a process involves a decision based on combinations of values of several conditions models representing: an overview of the processing the structure of the processing the flow of data into and out of the processes the detailed logic of the processes can be constructed 31 3 References HOFFER, J.A., GEORGE, J.F. and VALACICH (1999) nd ed., Modern Systems Analysis and Design, Benjamin/Cummings, Massachusetts. Chapter 1 and 8, WHITTEN, J.L. & BENTLEY, L.D. (1998) 4th ed., Systems Analysis and Design Methods, Irwin, Burr Ridge, Illinois Chapter 1 and 6 33