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) 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 • 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 between different parts of an organisation may lead to confusion and inefficiencies in storages

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 • Every entity is connected in the hierarchy can be broken down (decomposed) into the connected processes (functions) on the level below • Every process (function) in the hierarchy is a component of the process (function) to which it is connected on the level above

8. Why draw an FDD (organisational purpose)? • All human processes are done by combining a number of simpler processes (catching a ball example) • FDD enables us to identify the many simple individual processes which make up a complex system • Going up the hierarchy allows us to see how many different activities contribute to higher-order processes

9. Why draw an FDD (technological purpose)? • Computers can only perform very simple operations (read input, write output, add, compare); packaged software can do more complex tasks, but only what it is designed for • Therefore, any human information processing task needs to be decomposed into the simple operations which the computer can do or the standard tasks the package can do • FDD enables us to break complex human information processes into the simpler operations which a computer can do

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 • Breaking the development into component pieces allows different members of the development team to work simultaneously on different parts • An FDD enables the development team to break a large information system into separate components, while ensuring everyone knows where each component fits