G045 Lecture 07 DFD Context Diagrams (Data Flow Diagrams Level 0) Mr C Johnston ICT Teacher www.computechedu.co.uk

Session Objectives Understand what a context diagram shows, Know the common components of a context diagram, Be able to draw context diagrams for given scenarios,

Data Flow Diagrams Data Flow Diagrams (DFDs) show how data flows into, around and out of a system, They are made up of: External data sources, people or organisations the system interacts with (eternal entities) Flows of data, Processes, Data stores Diagrams are spilt into different levels each painting a more detailed picture of what happens within a system At level 0 they show the external data sources and how they interact with the system, At higher levels they show the how the data is adapted by the system and where it is stored.

Context (Level 0) Diagrams Show the external entities and how they interact with the system, Diagram takes the format of a box called _____ system with the entities scattered around the system box, Shape of the box will depend on the notation being used: If a rectangle is used for the system then ellipses are used for the external entities If an ellipse is used for the system then rectangles are used for the external entities One way arrows enter and exit the system joining it with the external entities to show the data flows, A label is then given to the arrow showing what data is flowing.

Examples Example context diagram using ellipse for system notation Example context diagram using rectangle for system notation

Drawing Diagrams Start by reading a scenario and summarising what is going on into a table Draw the diagram using the information in the table Its convention that arrows go down the diagram in order of what happens Data Flow External Entity Source / Recipient

Example Reporting day data is complied by a system at Stringer. Staff enter grades into the system for each student which includes their ID, a current working at grade and effort for a subject. The system stores them, compares with past data and generates a grade report for parents. Summary information is also generated for year heads showing subject grades for each student in the year and one for form tutors summarising their tutees performance. Data Flow External Entity Source / Recipient Student ID, working grade, effort STAFF Source Grade Information PARENTS Recipient Year group summary YEAR HEAD Tutor group summary TUTORS

REPORTING DAY SYSTEM STAFF PARENTS STUDENT DB YEAR HEAD FORM TUTORS Student ID, working grade and effort REPORTING DAY SYSTEM PARENTS Grade Information Student ID Student Details STUDENT DB YEAR HEAD Year group summary grades Tutor group summary grades FORM TUTORS

Exercises An insurance company system takes details from customers which includes personal, car and past claim data. The information acquired is complied and pasted onto an external broker which generates quotes. On return from the broker the best quote is formatted appropriately and sent to the customer. The university and college admission system (UCAS) handles applications to higher education by students in the UK. Students submit data to the system which includes personal details, estimated grades, courses and institutions they want to apply for and a personal statement. A tutor also submits a reference for each student into the system. The system compiles each students application and forwards it onto the institution applied for. Upon receipt the staff at the university scrutinise the application and return to UCAS an offer or rejection – this is then passed onto the student.

INSURANCE SYSTEM UCAS SYSTEM CUSTOMER BROKER TUTOR STUDENT INSTITUTION Personal, car, past claim data Customer Information INSURANCE SYSTEM Best Quote Quotes TUTOR Personal, est grades, courses and inst. data and personal statement UCAS SYSTEM Reference STUDENT Offer / Reject Response To Applicant Applicant Information INSTITUTION

Further Exercise For each of the further exercises listed below, read the case study and draw a level 0 (context) data flow diagram to show the main events in the current / proposed system. Further Exercise 1 Further Exercise 2

Further Exercise 1 Answer

Further Exercise 2 Answer

Assignment Link Draw a context diagram for KASBAH NEWS’ Current System. Start by drawing a table to identify all the external entities and dataflows, Then draw your diagram, Include a description of each external entity – Who / what are they How do they interact with the system, Why are they necessary, What information do they provide / receive and in what format

External Entity Description