1. Software Development Lifecycle- SDLC Design- using DFDs

2. SDLC - Recap

3. Design techniques Data Flow Diagram Flowcharts

4. Data Flow Diagram A data flow diagram looks at how data flows through a system. It shows: how information enters and leaves the system, what changes the information, where information is stored.

5. DFD 5 basic constructs: Data flows, Processes, Data Stores, External Entities, Physical Resources.

6. If the arrow from the store is single headed and points towards the process, this signifies a 'read' action Store Process External entity If the single arrow head points towards the data store then, this indicates a 'write' action, e.g. creating a record. An 'update' will consist of both a read and a write.

7. Data flows A data flow shows the flow of data from a source to a destination. Each data flow should be uniquely identified by a meaningful descriptive name (caption). Flow may move from ; an external entity to a process, from a process to another process, into and out of a store from a process, and from a process to an external entity. Flows are not permitted to move directly from an external entity to a store or from a store directly to an external entity.

8. Processes Processes are transformations, changing incoming data flows into outgoing data flows. The box has a top stripe that contains an identification number in the left, and the location (or the role carrying out the work) on the right (optional). The identification number is purely an identifier. It also helps to associate a high level process with its decomposed subprocesses.

9. Process The name of the process should describe what happens to the data as it passes through it. An active verb (verify, compute, extract, create, retrieve, store, determine, etc.) followed by an object or object clause is a suggested notation http://www.eis.mdx.ac.uk/staffpages/geetha/bis2030/ DFD.html

10. Data Stores A repository of data; e.g a database file The store may contain permanent data or temporary accumulations

11. External Entities (Source or Sink) A person or a part of an organisation which sends or receives data from the system Considered to be outside the system boundary (scope of the project).

12. DFD problem solving Draw a DFD for the following: A customer goes into a bookshop and asks for a particular book. The member of staff looks for the book in the online stock catalogue and reports that the book is sold out.

13. DFD Practise Every month, the Medical Centre receives a list of current drugs available from the drug companies. These lists are collated into a catalogue of drugs which is copied and given to each doctor.