1 CP2236 Information Systems Design Business & Technical System Options Required System Logical Data Flow Modelling Larger versions of slides 17,20,23,24 & 28 can be found at the end of of this handout

2 Business & Technical System Options Rare for only one solution to be possible. Analyst/Designer should be able to suggest several solutions to the business’s requirements. Business Systems Options (BSOs) provide a range of possible solutions for the business to consider. Each BSO may have more than one way of being implemented technically. These are known as Technical System Options (TSOs)

3 Business System Options (BSOs) Aim - To agree the functionality of the req. system. BSOs - done after the Requirements Catalogue (RC) has been formalised. Each entry in RC is considered, if any are excluded - document reasons. Develop 2-6 options. Using RC, project team establish & develop a list of : Minimum Functional Requirements (which all options must satisfy) & Non-Functional Requirements.

4 Functional Requirements - dictate what the system should do. What facilities are required & what activities the system should carry out: descriptions of required functions outline of reports - hard/soft copies on-line queries & updates data storage, retrieval & transfer, etc.

5 Non-Functional Requirements - address other facilities (limitations & constraints) Required Service/Performance Levels (response times for on-line functions, rate of data transfer) Security & Access Requirements Technical Constraints (make use of existing hardware) Project Constraints (system delivery deadlines & cost limits) Quality of user interfaces (how intuitive and easy to learn, and to use the technology to perform the task)

6 BSOs - consider the following factors: Approximate cost of each option Development time scale Known technical constraints Organisation of the system - types of access (on-line or off-line), interfaces with other systems Approximate data and transaction volumes Training requirements Benefits & impact on the organisation

7 Business System Options Upto 3 shortlisted. Each Option presented formally to the management. Strengths & Weaknesses explained to facilitate a decision. Opportunity to reassess the viability of the project (to carry on / cancel it). Selected BSO could be one option or an hybrid. Document selected BSO (reasons for selection & rejection others). Form the basis for the rest of the project and for the final system.

8 Technical System Options (TSOs) Addresses how the req. system is to be implemented. Define the TSOs: Identify constraints - external & internal Develop outline options (Up to 6) Select 2 or 3 main options for detailed dev’t Refine selected options - check performance Select the final TSO: Present options Fully document selected TSO (rationale for the selected option)

9 Technical System Options (TSOs) Each Full TSO contains 5 main parts: Technical environment description System description Impact analysis Outline development plan Cost / Benefit analysis

10 Current System DFDs There are 2 versions of this: 1.Current PHYSICAL DFD Representation of the current system as it is. May show letters, filing cabinets, manual data stores etc. 2.Current LOGICAL DFD Removes all physical references to the system. The process is referred to as Logicalisation.

11 Steps in Logicalisation (revision) Replace Physical Data Stores with main Logical Data Stores. Remove Transient Data Stores Remove/separate out processes that cannot be automated and/or require subjective decisions or will remain subjective. Remove processes which only reorganise data (e.g. sorting).

12 Combine processes which are joined by a data flow only, and which form part of the same or a very similar process Combine processes performing the same functions (appear separate only because of physical location). Minimise Data Flow Contents. Remove all physical references. Remove processes which do not alter data (ad hoc retrievals without creation or update. Remove processes which exist due to tradition or politics

13 Required System Logical DFMs: Current Physical DFM Current Logical DFM Required Logical DFM Requirements Catalogue Selected BSO

14 Required System Logical DFDs The broad aim is to take the current logical DFD and to map the Requirements Catalogue and BSO’s on to it.

15 Required System Logical DFMs - MethodStep1 Decide which processes on the current logical DFD are needed, then include these on the required logical DFD. Step 2 Look at the requirements catalogue, see what new processes are needed to meet the new requirements, add these to the required logical DFD. Generally, any process that could be done by computer is a candidate for automation. Any process that requires human judgement must be ruled out.

16 Current Logical Context Level DFD:

17 Current Logical Level 1 DFD:

18 Requirement Catalogue entries: 1.Manager can produce a list of members monthly, and then select members who will be eligible for monthly bonuses. 2.Generate and send monthly bonus letters to selected members. 3.Incorporate purchasing of new videos from suppliers - an order for new videos is generated and sent to suppliers. Suppliers send the invoice and the videos to the store. A payment is sent to the supplier on receipt of the invoice.

19 Requirements Catalogue Requirements 1 & 2 A new process (7) is added to incorporate requirements 1 & 2. The existing Loan details and Member data stores are included. Members details are sent to the manager and a bonus list is generated. The bonus letter is sent to the customer.

20 Process 7 DFD

21 Required System Logical DFMs - Method Step3 To maintain data, new data stores may need to be added. Identify these and add to the required logical DFD.

22 Requirements Catalogue Requirement 3 Another process (8) is needed to incorporate Requirement 3 into the logical DFD. In this example, a new data store ‘Video order’ is also added.

23 Process 8 DFD

24 Required Logical Level 1 DFD:

25 Context Diagram The Context Level required system logical DFD. follows same principles as for current physical and current logical DFDs. Any Level 1, Level 2 diagrams should balance with the context diagram.

26 Required Logical Context Level DFD:

27 Exercise Incorporate the following entry from the Requirements Catalogue into the required system DFM Requirements Catalogue Storecard holders should have the facility to close their accounts.

28 Requirements Catalogue Storecard holders should have the facility to close their account.

29 PRINT INSTRUCTIONS Handout- pp 1-16,18,19,21,22,25,26,27 2 per page for 17,20,23,24,28