IMS1805 Systems Analysis Topic 3: Doing analysis (cont from Monday)

2 Recap of last lecture The importance of understanding the purpose of analysis Some important purposes: Organisational; Technological; Development team The purposes behind process models (FDD/DFD)

3 Agenda Aim: To develop further your understanding of the main purposes for which IS analysis is done To identify the purpose of diagram-based data analysis techniques in IS To work through some examples of the use of process-oriented and data-oriented analytical techniques

4 2(c) (Continuation of Monday) Why draw data models? Data models enable us to focus on: the information which needs to be stored about things in a system; and the information inter-connections which have to maintained between these things Entity-relationship diagrams tell us what things (entities) we need to store information about, and what the characteristics are of the relationships between these things

5 Data in organisations Organisations always have to store data about things (entities) Every entity has many attributes associated with it Key data items may be used very widely across an organisation for a huge range of purposes (often unrelated) by a wide variety of people Inconsistencies in data and data storage between different parts of an organisation may lead to confusion and inefficiencies in storages Data may be more stable than processes, which may have to be changed often to meet new needs

6 Analysing data in organisations We analyse entities: To identify all the entities which have to be stored and the attributes of each one To define what linkages (relationships) must be kept between these entities and what rules apply to these relationships By doing this, we aim to: Develop a sound basis for design and construction of databases to store information consistently and non- redundantly Identify areas of shared data/overlapping and conflicting data needs Determine the rules for validating data in databases

7 2(c): Data Models: Reminder of E-R basics (covered in database unit) Entities are represented as boxes Relationships or connections between entities (indicating shared data elements) are shown by lines connecting the entities Information about the nature of the relationship is written next to the connecting line (or in a diamond-shaped box on the line)

8 Why draw an E-R diagram (organisational purpose)? There is always massive overlap and duplication in data storage needs in different parts of an organisation An organisation-wide E-R Diagram can show the extent of shared data needs/uses; they enable development of data structures in which data can be entered and stored in one place, but used by many different people to meet different needs The relationships showed in an E-R diagram allow us to see what connections need to be made to enable queries between data entities

9 Why draw an E-R Diagram (technological purpose)? Relational databases are now the single dominant form of technology used for storage of data Relational databases require the developer to identify schemas, tables, fields and data validation rules for entering data into the database Database query languages require relationships to be specified between database tables to permit queries which connect data across the database tables E-R diagrams provide a framework and ‘rules’ for database development

10 Why draw an E-R diagram (team purpose)? Development of a complex system will include storage of many data items in complex data structures – multiple databases/database tables/database fields/etc Identifying the entities and their attributes helps all development team members keep track of the key data items being recorded by the organisation An E-R diagram provides a central reference point on system data for all development team members

11 Using Process and Data Models See examples discussed in class