IMS1805 Systems Analysis

1. IMS1805Systems 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