Section 08Data Dictionary - Structures & Elements 1 08 THE DATA DICTIONARY Structures & Elements And Franchise Colleges By MANSHA NAWAZ

Section 08Data Dictionary - Structures & Elements 2 Introduction We've seen how to build up a useful model of a system using DFDs. The technique of explosion within DFDs is a powerful way of breaking a complex problem down into a number of simpler problems. However, we still haven't reached the level of detail that would be needed by a developer to actually build the system. This is provided by the Data Dictionary. A Data Dictionary is a collection of further details about everything on a set of DFDs, not only about data, but also about processes.

Section 08Data Dictionary - Structures & Elements 3 Recording Data in the Data Dictionary The data parts of DFDs are data flows and data stores. On the DFD we have just a name for these, so we need to record the content and structure of these before we can develop software. For our logical model, we want a way of describing the data that will accommodate any physical implementation. This is done by describing the data in terms of data elements and data structures.

Section 08Data Dictionary - Structures & Elements 4 The Data Dictionary it is a receptacle for storing information on all system items –data stores –data flows –processes –external entities it contains a logical description

Section 08Data Dictionary - Structures & Elements 5 –Data Dictionary Data Stores and Flow lecture 08 lecture 08 –Structures & Elements Data Stores and Flow –Usage lecture 09 lecture 09 Process Descriptions –Mini Specs and Sample Screen Shots lecture 10 lecture 10 –NORMALISATION lecture 11 lecture 11 Database Tables derived from Data Store Descriptions Document : Design Specification

Section 08Data Dictionary - Structures & Elements 6 THE DATA DICTIONARY : Data Structure & Elements SYSTEMS DESIGN

Section 08Data Dictionary - Structures & Elements 7 Aim –to be able to describe data in terms of its constituent structures and elements Objectives –to identify indivisible data items –to record elements using a given syntax –to identify collections of data items –to record structures using a given syntax Learning Aims

Section 08Data Dictionary - Structures & Elements 8 the need to describe data a data hierarchy data elements data structures Yourdon’s data notation Lecture Outline

Section 08Data Dictionary - Structures & Elements 9 the DFD gives a logical view of a system’s functionality a DFD provides use with DATA STORES & DATA FLOWS the designers/programmers will need to know the logical composition of the data what it is and not the actual values Describing Data

Section 08Data Dictionary - Structures & Elements 10 Each DATA STORE requires a data description comprising of its Data Structures & elements Each DATA FLOW may requires a data description comprising of its Data Structures & elements (only record for dataflow whose data description is different from its datastore) Starting Point:

Section 08Data Dictionary - Structures & Elements 11 data seen as a two level hierarchy data elements –smallest logical item data structures –collection of elements –collection of structures –collection of both Data Structure Data Element A Data Hierarchy

Section 08Data Dictionary - Structures & Elements 12 the items of data within the problem domain that can’t be further divided for example an address –15 High St, M’boro, Cleveland, TS4 5KL this can be broken down into elements –a house number, a road, a town, a county and a postcode each of these can’t be further divided Data Elements

Section 08Data Dictionary - Structures & Elements 13 the items of data that can be further sub- divided the data item ‘address’ is a structure because it can be further divided into meaningful data items here the structure consists of a number of elements but it is possible to have structures nested within structures Data Structures

Section 08Data Dictionary - Structures & Elements 14 Structures: ADDRESS= houseno + road + town + county + postcode Elements: houseno= 1{char}3**usually numeric road= 1{char}15 town= 1{char}10 county= 1{char}10 postcode= 6{char}7 ** format $$# #$$ where each $ = [A..Z] each # = [0..9] often the elements are described using the types found in databases - char, integer, real, boolean, date Example

Section 08Data Dictionary - Structures & Elements 15 X = YX is composed of Y X + YX and Y (X)X is optional item j {X} k iterated item, j/k low/upper limit [X | Y]item to be selected from X or item **comment Yourdon’s Notation

Section 08Data Dictionary - Structures & Elements 16 this division of data in elements and structures allows analysts to re-use defined items other structures can have the structure ADDRESS as a constituent part but the elements that make up ADDRESS and ADDRESS itself need only be defined once Avoid Redundancy

Section 08Data Dictionary - Structures & Elements 17 Recording Elements & Structures check each data item in the system –identify all elements & structures create a list of each type and record –name elements lower, STRUCTURES upper case –description one sentence english text –composition use given notation

Section 08Data Dictionary - Structures & Elements 18 Contd. –aliases other names used, delivery note/despatch note –discrete values or continuous range limits NZ = New Zealand or –default value preset value on creation –validation information if title = Mr then sex = Male –related data items houseno, associated with structure ADDRESS

Section 08Data Dictionary - Structures & Elements 19 –Data Dictionary lecture 08 lecture 08 Data Stores - Structures & Elements lecture 08 lecture 08 –Start by listing each DATA STORES –For each data store list structures and elements –Draft a form view for the data store Data Flow - Structures & Elements lecture 08 lecture 08 –Start by listing each DATA FLOW –Copy and paste the related data store structures and elements –Cut or delete the structures and elements which are not required –Draft a form view for the data flow. Data Stores and Flow Usage lecture 09 lecture 09 Process Descriptions lecture 10 lecture 10 Document : Data Dictionary

Section 08Data Dictionary - Structures & Elements 20 Please Note: Ascent allows you to record the Data Dictionary Structures and Elements and a guide has been produced DD in Ascent.DD in Ascent Unfortunately Ascent is weak when producing data dictionary content for a report. So feel free to utilize MS Word when creating your Data Dictionary Structures and Elements.

Section 08Data Dictionary - Structures & Elements 21 Summary For each Data Store describe logical data data elements data structures notation minimal redundancy Self Study review the lecture complete exercises from the course workbook Summary & Self Study

Section 08Data Dictionary - Structures & Elements 22 Further Reading Notes from Annette Marshall 257/SDV/SDevWk5.dochttp://outranet.scm.tees.ac.uk/users/u /SDV/SDevWk5.doc