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) 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