Systems Analysis Essay Example

Systems Analysis Essay Systems analysis can be defined as a disciplined process, which begins with the establishment of user requirements for a given application and concludes with the implementation of fully operational system The main stages of systems analysis are often referred to as the system life cycle. The following sections give a brief overview of their functions within the systems analysis process. Feasibility study The aim of this stage is to establish whether or not a proposal for the computerisation of a particular application is worthwhile or feasible. In simple terms, the feasibility study has to answer questions such as: Will computerisation achieve the users objectives?; We will write a custom essay sample on Systems Analysis specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Systems Analysis specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Systems Analysis specifically for you FOR ONLY $16.38 $13.9/page Hire Writer What type of system will be most suitable?; Will it be financially worthwhile? System investigation and design Assuming that the feasibility study produces a recommendation to proceed with computerisation of an application, then before any system specification is produced, an analysis has to be made of the processes and procedures involved in the application under consideration. For example, an analysis of Sales Order Processing should identify how orders are received, the order forms used and the procedures necessary to fulfil orders. Analysis is not simply the recording of an application as it currently operates through a variety of information gathering methods such as interviewing and observation, the requirements of a new system should be identified. Although the needs of the organisation are of obvious importance, employees are more likely to be concerned with matters of job satisfaction and working conditions. Successful implementation of a computerised system requires a great deal of work, involvement and willingness to co-operate by everyone concerned. If staff feel that their views have been considered such co-operation is more likely. Although users views are Important an outside observer can often identify problems with current practice which have never been questioned. A systems analyst from outside the firm needs therefore, to possess qualities of tact and diplomacy if his or her views are to be considered. The process of design should produce a complete picture of * the input, * processing, * storage and * output requirements of the new system. The picture will include * narrative descriptions, * flowcharts illustrating clerical procedures, * data flows and * the role of the computer in broad outline. The design of a computerised system should include as many improvements suggested in the investigation stage as is practicable and it will almost certainly be necessary to question tiers further when, for example, problems arise in the implementation of particular system requirements. Compromises will have to be made between what is desirable and what is practicable. Management and users may have specified requirements during the investigation stage, which prove either too expensive or extremely difficult to satisfy. System implementation System implementation or going live involves a range of preparatory. The main activities are as follow: * Development and/or testing of software. If an off the shelf system is chosen, then no development time is necessary, but testing is still vital. * File conversion. This is probably the most time-consuming activity in that all data relating to the application, which is currently held in manual files, has to be encoded onto the chosen magnetic storage medium. accuracy is vital and both software and clerical checking procedures should be employed. * Staff training and education. This may take a variety of forms but may be part of the proposals put forward by the chosen supplier. It is an extremely important activity if the systems effectiveness is to be maximised and if staff are to feel happy and confident in its operation. * Introduction of new clerical procedures. If the whole system is to function correctly, the computer processing aspect has to be supported by the clerical procedures designed to work with it. Part of staff training, therefore, has to be dedicated to purely clerical tasks such as the preparation of input data or source documents. * Choice of a changeover or going live plan. A number of alternatives are available and each has costs and benefits associated with it. Parallel running, requires that the old and new systems be operated alongside one another until the new system is fully tested. This minimises the risks consequent upon system failure, it is an expensive option in that it involves a great deal of staff time. Direct changeover is less expensive if the new system works but failure could mean catastrophe for the business. The plan used will depend on a number of factors, for example, the importance of the system to the success of the business. System maintenance After its initial introduction a system should be flexible to the changing needs of the business. An allowance for the businesss expansion should be made in the original system specification and the supplier should be able to satisfy those expansion needs as and when necessary. Equally, advances in hardware technology and the sophistication of software mean that a system soon becomes outdated. Even if a business chooses not to take advantage of improved software, hardware is likely to become less reliable and will need replacement after about five years of business use. Agreements on software and hardware maintenance should be established with the supplier and formalised in the contract signed by purchaser and supplier. The Feasibility Study The purpose of a feasibility study is to determine whether or not the purchase of a computer system can be justified. The study has to answer two fundamental questions: 1. Can the envisaged applications be carried out by a computer system more efficiently than with existing facilities?; 2. Will a computer system be economically viable?. Since the early 1 970s, prices of all types of computer system have fallen dramatically and their power has increased to such a degree that, for example, microcomputers challenge the minicomputer in their range of applications. This may be part of the reason why many organisations find it difficult to justify undertaking a detailed feasibility study and argue that no matter how limited their needs there is a computer system to satisfy them at a cost-effective price; it is only necessary to decide on its best application(s). Although this is an understandable view, it should be remembered that any item of equipment should be justified in terms of its costs and benefits to the business and that a computer system should be no exception. Although there are few businesses, which cannot benefit from computerisation at all, the process of carrying out a feasibility study disciplines the purchaser to think carefully about how it is to be used. In modifying the purpose of a feasibility study, the previous questions can be replaced by the following: 1. Which applications can be computerised to give most benefit to the organisation?; 2. What type of computer will be required?; 3. What are the likely acquisition and running costs?; 4. What are the likely implications, especially those concerning personnel and organisational procedures?. Pressures for computerisation There are many and various pressures which can trigger the thought of using a computer, either for the first time or, where a computer is already installed, for other applications still operated manually. Some examples are as follow: i. A business is expanding and to cope with the increased workload it appears that the only the alternative to computerisation is increased staffing. ii. A business is growing at such a rate that more information is needed to manage it properly. To obtain the information manually is too time-consuming and by the time it has been gathered is probably out-of-date. iii. Staff are being asked to work regular and increasing amounts of overtime and backlogs of work are building up. iv. Customers are complaining about the speed and quality of the service provided. v. Where stock is involved, it is difficult to keep track of stock levels and while some customer orders cannot be filled because of stock shortages, other stock is gathering dust on the shelves. vi. A great deal of advertising literature is constantly reminding business management that they are out-of-date and at a disadvantage with their competitors. vii. Other businesses providing a similar service use a computer. Examples (i), (ii) and (iii) suggest that the business is operating successfully and needs to take on extra staff or streamline its systems. Examples (iv) and (v) may be symptomatic of generally poor business management and in such cases, computerisation alone may not solve the problems. Examples (vi) and (vii) may tempt the management to computerise simply to keep up with the Joness. Although a computerisation programme resulting directly from one or more such pressures may be completely successful and worthwhile, the pressure itself should not be the reason for computerisation. Instead, management should establish the organisational objectives they wish to achieve through computerisation. Establishing objectives for computerisation It is important for management to establish what they are trying to achieve in terms of the overall objectives of the business and in the light of this, the objectives of the systems, which contribute to their achievement. For example, two major business objectives may be to improve the delivery of customers orders and to minimise the stock levels, which tie up valuable cash resources. The achievement of these objectives may involve contributions from several different information processing systems and the list may include the following. * Stock Control records stock movements and controls stock levels. * Purchasing responsible for the ordering of new supplies from suppliers. * Sales Order Processing receives customers orders and initiates the process of order fulfilment. * Purchase Ledger the accounting record of amounts owed and paid to suppliers of stock. * Invoicing the production of invoices requesting payment from customers for goods supplied. * Sales Ledger the accounting record of amounts owing by and received from customers for goods supplied. These and other applications within a business are interconnected by the information, which flows between them. Such connections can be illustrated with the use of data flow diagrams (DFD), which are described in Chapter 25. Establishing priorities for computerisation The applications which are going to bring greatest benefit to the business should be computerised first. Establishing individual system objectives The objectives of the relevant application must first be clearly understood. The following is a typical list for stock control serves to illustrate the definition of such objectives. * To maintain levels of stock which will be sufficient to meet customer orders promptly. * To provide a mechanism which removes the need for excessive safety margins of stock to cover customer orders. This is usually effected by setting minimum stock levels, which the computer can use to report variations below these levels. * To provide automatic re-ordering of stock items which fall below minimum levels. * To provide management with up-to-date information on stock levels and values of stocks held. Contents of the Feasibility Report The Feasibility Report should contain the following sections: Terms of reference These should set out the original purpose of the study, as agreed by management and detail the business objectives to be achieved, for example: (i) the improvement of customer service, such that orders are delivered within 24 hours of order receipt; (ii) the provision of more up-to-date management information on current stock levels and projected customer demand; (iii) a tighter control of the businesss cash resources, primarily through better stock management. Applications considered for computerisation The applications which may assist the achievement of the business objectives set out in the Terms of Reference are listed, for example: stock control; purchasing; sales order processing; invoicing; accounts. System investigations For each application under consideration there should be: * a description of the existing system; * an assessment of its good and bad points. For example, the sales order processing system may be slow to process customer orders and this results in poor delivery times, which in turn causes customers to take away their business; * an estimate of the costs of the existing system. For example, apart from the cost of staffing, an estimate has to be made of the cost of lost business, which could be avoided with an improved system. Envisaged system requirements This section should detail, in general terms, those aspects of each application which need to be improved and a broad outline of how each system may operate following computerisation. Costs of development and implementation These will include both capital costs and revenue or running costs. Capital costs are likely to be incurred for the following: (i) computer hardware; (ii) systems software and software packages (either off-the-shelf or tailor-made); (iii) installation charges for hardware and software; (iv) staff training. Revenue costs include those for the maintenance and insurance of the system. In addition, unless there are existing computer specialists in the organisation, additional suitable staff may need to be recruited Timescale for implementation This will depend on the scale of the operation, the type of application and whether or not packaged software is to be used. Expected benefits These are more difficult to quantify than the costs but may include, for example: * estimated savings in capital expenditure on typewriters and photocopiers; * more efficient stock management allows customer service to be maintained whilst keeping stock levels lower. This releases valuable cash resources and reduces possible interest charges on borrowed capital; * expansion in business turnover, without the need for extra staff and reduced overtime requirements. Other considerations The staff have to support any development for it to be properly successful and this usually means consultation at an early stage in the feasibility study and the provision of a proper staff-training programme. Customers must also be considered. For example, when a customer receives a computer produced invoice it should be at least as easy to understand as the type it replaced. Assuming that the feasibility study concludes that the proposed computerisation is worthwhile, according to the criteria set out in the report, then more detailed investigation and design can follow. System Investigation and Design Introduction If the feasibility report gives the go-ahead to the computerisation project, then a more detailed investigation of each candidate system begins. The facts gathered about each system will be analysed in terms of their bearing on the design and implementation of a computerised version. The objectives of the analysis are to gain a thorough knowledge of the operational characteristics of the current system and to settle, in a fair amount of detail, the way in which a computerised system will operate. It is extremely important that the new system does not simply computerise existing procedures. The design should, as far as possible, ignore existing departmental structures, which may inhibit the introduction of different and improved procedures. The aim of the investigation and design process is to produce a specification of users requirements in documented form. This is referred to as the Statement of User Requirements and will be used to tender for supply of hardware and software. Fact-finding methods There are several methods, which can be used to gather facts about a system: (i) interviewing; (ii) questionnaires; (iii) examination of records and procedure manuals; (iv) examination of documents; viii. observation. Each method has advantages and disadvantages and the method or methods chosen will depend on the specific circumstances surrounding the investigation, for example, the size of the business, the number of staff employed and their location and distribution. Interviewing This method has much to recommend it, in that the facts can be gathered directly from the person or persons who have experience of the system under investigation. On the other hand, a business with a number of geographically distributed branches makes the process of extensive interviewing expensive and time-consuming. Further, interviewing skills need to be acquired if the process is to be effective. The interviewer needs to know how to gain the confidence of the interviewee and ensure that the information, which is given, will be of value in the design of the new system. Questions need to be phrased unambiguously in order that the interviewee supplies the information actually required and a checklist of points will help to ensure that all relevant questions are asked. Of course, the interview may need to stray from the points in the checklist, if it becomes apparent that the interviewee is able to provide relevant information not previously considered. For example, clerical procedur es may be designed quite satisfactorily but may be made less effective because of personality conflicts between staff. Such tensions may only be revealed through personal interview. The interviewer also needs to detect any unsatisfactory responses to questions and possibly use alternative methods to glean the required information. Unsatisfactory responses include: * Refusal to answer. Such refusal may indicate, for example, that set procedures are not being followed and that the member of staff does not wish to be incriminated. * Answer with irrelevant information. It may be that the question is ambiguous and has to be re-phrased in order to elicit the required information. * Answer with insufficient information. If a system is to be designed which covers all foreseeable user requirements and operational circumstances, it is important that the analyst has all relevant information. * Inaccurate answer. The interviewer may or may not be aware that an inaccurate answer has been given but it is important that other sources of information are used to cross-check answers Questionnaires Questionnaires are useful when only a small amount of information is required from a large number of people, but to provide accurate responses, questions need to be unambiguous and precise. The questionnaire has a number of advantages over the interview: * each respondent is asked exactly the same questions, so responses can be analysed according to the pre-defined categories of information; * the lack of personal contact allows the respondent to feel completely at ease when providing information, particularly if responses are to be anonymous; * questionnaires are particularly suited to the gathering of factual information, for example, the number of customer orders received in one week; * it is cheap, particularly if users are scattered over a wide geographical area. A number of disadvantages attach to the use of questionnaires: * questions have to be simple and their meaning completely unambiguous to the respondents; * if the responses indicate that the wrong questions were asked, or that they were phrased badly, it may be difficult to clarify the information, particularly if the respondents were anonymous; * without direct observation it is difficult to obtain a realistic view of a systems operation. The questionnaire often provides only statistical information on, for example, volumes of sales transactions or customer enquiries. Examination of records and procedure manuals If existing procedures are already well documented, then the procedure manuals can provide a ready-made source of information on the way procedures should be carried out. it is important to realise that procedures detailed in manuals may not accord entirely with what actually happens. The examination of current records and the tracing of particular transactions can be a useful method of discovering what procedures are carried out. Special purpose records, which may involve the ticking of a box when an activity has been completed, can be used to analyse procedures, which are causing delays or are not functioning efficiently. The use of special purpose records imposes extra burdens on staff who have to record procedures as they happen and the technique should only be used when strictly necessary. Examination of documents It is important that the analyst examines all documents used in a system, to ensure that each: * fulfils some purpose, that is, it records or transmits information which is actually used at some stage. Systems are subject to some inertia, for example, there may have been a one-off requirement to record and analyse the geographical distribution of customers over a single month and yet the summary document is still completed because no-one told the staff it was no longer necessary; * is clear and satisfies its purpose, for example, a form may not indicate clearly the type of data to be entered under each heading. In any case, it may well require re-designing for any new system which is introduced. The documents, which should include, for example, source documents, report summaries, customer invoices and delivery notes, help to build a picture of the information flows which take place from input to output. Observation It is most important to observe a procedure in action, so that irregularities and exceptional procedures are noticed. Observation should always be carried out with tact and staff under observation should be made fully aware of its purpose, to avoid suspicions of snooping. The following list details some of the features of office procedures and conditions, which may usefully be observed during the investigation: * office layout this may determine whether the positioning of desks, filing cabinets and other office equipment is convenient for staff and conducive to efficient working; * work load this should indicate whether the volume of documents awaiting processing is fairly constant or if there are peak periods of activity; * delays these could show that there are some procedures which are constantly behind schedule; * methods of working a trained observer can, through experience, recognise a slow, reasonable or quick pace of working and decide whether or not the method of * working is efficient. It is important that such observations should be followed up by an interview to obtain the co-operation of the person under observation; * office conditions these should be examined, as poor ventilation, inadequate or excessive temperatures, or poor lighting can adversely affect staff efficiency. Often the observation will be carried out in an informal way but it may be useful on occasion to, for example, work at a users desk, so as to observe directly the way that customer orders are dealt with. It is important to realise that a user may put on a performance whilst under observation and that this reduces the value of the information gathered. Documenting the results of analysis A number of standard approaches, apart from narrative description, can be used to document the result of the system analysis, including: data flow diagrams (DFDs); organisation charts system flowcharts. Their applications are illustrated in the following section, which examines the categories of information, which need to be gathered and recorded during a system investigation. Categories of system information The major categories of information which need to be gathered involve: * functional relationships and data flows; * personnel and jobs; * inputs; * processes; * outputs; * storage. Functional relationships and data flows A business has a number of functional areas, such as Sales, Accounts, Stock Control and Purchasing, each having its own information system. However, the computerisation of a system in one functional area cannot be carried out without considering its effects on the rest of the business. Information systems within a business interact with and affect one another. The business, as an entity, also interacts with and is influenced by individuals and organisations in the surrounding environment and the businesss individual information systems should be co-ordinated to allow the achievement of overall business objectives. The data flows between individual functional areas can be illustrated with the use of a data flow diagram. Personnel and jobs It is possible to design a computerised system without involving staff, but it is likely to be less successful, partly because users can provide valuable insights into the practical aspects of system operation and partly because they will feel less motivated if they have had little or no influence on the final design. A formal organisation chart can be used to gain an overall picture of staff relationships and responsibilities but it should be borne in mind that designated and actual job responsibilities can differ radically. For example, it may turn out that a junior sales clerk is carrying out the checking of orders, which should be the responsibility of the sales supervisor. Thus, it may be necessary for the analyst to draw an alternative informal organisation chart to show the actual working relationships of staff. An example is given Apart from identifying working relationships between staff, it is useful to draw up brief job descriptions so that consultation on individual system procedures can take place with the appropriate staff. For example, a job description for a sales clerk may include the following activities: completion of standard order forms; checking stock availability; notification of orders to accounts. Therefore, although the sales departmental manager may have knowledge of such procedures, the sales clerk will have practical experience of their operation and should be consulted. System inputs A number of details concerning the data inputs to a system need to be established: * source. It may, for example, originate from a customer, a supplier, or another department in the business; * form. The data may arrive, for example, by telephone, letter, or a standard form such as an order form or suppliers invoice; * volume and frequency. For example, the number of orders received daily or weekly; * contents. For example. the individual items of data which appear on a suppliers invoice. Such information will allow the analyst to make recommendations on the most appropriate methods of computer input. The design of appropriate input methods also has to take account of several tasks involved with the collection and entry of data to a system: * recording. For example, the completion of a customer order form following receipt of a customer order by telephone; * transmission. For example, the order details may need to be transferred to another department or branch of the business for encoding and computer processing or they may be keyed in directly at the point of collection; * visual checking. It may be, for example, that a customer order has no quantities entered; * encoding. Verification procedures need to be designed to prevent transcription errors when data is encoded onto a computer storage medium for processing; * validation. Data is checked by a data vet program against set limits of validity, for example, account numbers may have to fall between a particular range of values. Thus, decisions need to be made concerning: (i) data collection procedures; (ii) methods for the transmission of data to the place of processing; (iii) data entry, data verification and data validation procedures. Data collection The designer needs to be aware of the available input technologies. These can be divided into two categories, keyboard entry and data capture technologies such as bar code reading, optical character reading (OCR) and optical mark reading (OMR), which allow direct input to the computer from specially designed input forms. Keyboard entry This is the most common method of input and requires the transcription of data from source documents. These can be designed to minimise the possibility of transcription errors at the data collection stage. Direct input Bar codes are pre-encoded and are thus immune from errors of transcription (assuming that the bar code is correct in the first place). Optical mark reading requires that pencil marks be used to indicate particular values from a limited set on a pre-designed form. Although no keyboard entry is required, mistakes may be made by the originator of the document and good design is therefore important. Data transmission It may be that no data transmission is necessary because the data is processed at the point of collection. For example, customer orders may be recorded on order forms at the sales desk and then taken into the next room for keying into the computer. Alternatively, the data may have to be transmitted some distance, perhaps to another floor of the building or to another building some miles away. A fundamental decision has to be made, whether to localise processing at the points of collection, or to use a central facility with data communications links from each location. Data entry The data entry method chosen will depend on the data collection methods used and may involve keyboard transcription from source documents or data may be captured directly from bar codes, OCR or OMR type documents. Where keyboard transcription is used, verification and validation procedures are likely to be interactive, in that the data entry operator has to respond to prompts on screen and make corrections as and when the system indicates Most small business computer systems will be used for on-line processing, where transactions are processed immediately with master files at the data entry stage. Consequently, validation and verification have to be carried out immediately prior to the processing of each transaction. On-screen verification At the end of each transaction entry, the operator is given the opportunity to scan the data on the screen and to re-enter any incorrect entries detected. This usually takes the form of a message at the bottom of the screen, which is phrased in a way such as Verify (yes or no). On-screen validation Character, data item and record checks, such as range and mode checks, can be made each time the RETURN key is pressed during data entry. For example, the screen may prompt for the en-try of an account number, which must be 6 digits long and be within the range 000001 to 500000. Any entry which does not conform with these parameters is erased and the prompt re-displayed for another attempt. Appropriate screen dialogue to allow the data entry operator to enter into a conversation with the computer is a crucial part of the input design process and is dealt with as a separate topic in Chapter 21. Batch data entry The type of keyboard transcription used will be affected by the type of input data. Where, for example, files only need to be updated weekly, transaction data may be batched and entered onto magnetic disk for processing at a later stage in one update program run. System processes All the clerical and machine-assisted processes, which are necessary to achieve the desired output from the given inputs, need to be identified. This will allow the systems analyst to determine the role of the computer in the new system, the programs necessary to take over the processing stages and the changes needed to clerical procedures, before and after computer processing. There are many instances when the processing requires not only the input data but also data retrieved from files. For example, to generate a customer invoice requires: i. input data concerning commodity codes and quantities ordered; ii. data from the stock master file concerning prices of items ordered by reference to the input commodity codes; iii. customer details from the customer master file. The above processes can be completely computerised but other processes may require human intervention. For example, before a customer order is processed, the customers credit status may need to be checked and referred to a supervisor before authorisation. Non-standard procedures Most processes will follow standards suitable for their particular circumstancesIt is important, however, that the investigation identifies and notes any non-standard procedures. For example, what procedure is followed when there is an insufficient quantity of an ordered item to completely fulfil a customer order? It may be that some customers will take part-orders, whilst others require the full quantity of an item or none at all. If non-standard procedures are needed, it is important to know their complexity, how often they are used and what extra information is required. Ideally, a system should be designed to cope with all possible circumstances, but cost sometimes forces a compromise. Document flow System flowcharts can be used to model the movement and interaction of documents and the data they record, as well as the processes involved. In order that the involvement of each section, department or personnel grouping in the processes can be identified, the system flowchart is divided into columns representing these divisions of responsibility. A system flowchart may use a range of standard symbols, which are illustrated in Figures below. A number of standards exist for the drawing of system flowcharts and the range of symbols used depends on which stage of the investigation and design process has been reached. For example, in the early stages of investigation of an existing manual system, there will be no representation of computer methods of input, processing, output or storage. At a later stage, when computer methods are being considered, it will be necessary to use suitable symbols in the flowchart Flow Chart Symbols Figure illustrates example of a manually operated order processing and invoicing system. The Figure illustrates example of a batch processing stock file update of a stock master file. Notice the sorting and validation stages, which are essential to batch processing systems Most business systems require alternative actions to be taken dependent upon some variable condition or circumstance. For example, 15 per cent customer discount may be allowed if the invoiced amount is paid within, say, 14 days of the invoice date, after which time all discount is lost Batch Processing Stock File Update Of A Stock Master File. In order that computerised and non-computerised processes can be properly designed, the investigation must identify all: * decisions made during system operation; * conditions and circumstances which lead to alternative decisions; * actions to be taken following a decision. Figure represents the computerised aspects of a similar system, but does not show detail procedures needed to prepare, for example, the data for input or the distribution of output. A computerised system must have the necessary clerical procedures to support it. Some decisions and consequent actions will need to be documented for clerical procedure guidelines, whilst others which involve computer processing will form part of program specifications used in program writing or as bases for choice of packaged software. System outputs * output design first requires identification of the following: * data items required as output. Some may be revealed in the existing system, whilst others may be requested by users as being desirable in any new system; * form of the output, for example, whether or not printed copy is required; * volume of data with each output and the frequency of the output. This information assists decisions on the type and number of output devices required. On-line orderprocessing Based on the above information, the following tasks can be carried out: i. selection of an appropriate output device to display or communicate the outputs. ii. designing output screen and document layouts. System storage (files) The storage of historic and current information is a vital part of any business system. For example, to produce a payslip not only requires transient input data concerning hours worked and sickness days but also data on rate of pay, tax code, deductions of tax and superannuating to date etc., which are held in the payroll master file stored on magnetic disk. Information on the contents of files will be gathered from existing manual files, together with responses from users regarding the output requirements of any new system. If packaged software is to be used then the contents of files will be dictated by the package, in which case some data item types may be surplus to requirements, whilst others which are required may not be available. File contents Each file consists of a number of logical records, each of which has a number of associated data items. For example, each stock record in a stock master file may include: Stock Code; Description; Unit Price; Minimum Stock Level; Re-order Quantity; Quantity in Stock. File organisation and access This concerns the logical ordering of records within a file. Database management systems (DBMS) An increasingly popular alternative to traditional file processing systems is to construct databases controlled by a DBMS. The design process requires that data is analysed according to subject area, for example, raw materials or staffing, rather than by department or functional area. Choice of storage device Choice is concerned with storage capacity, mode and speed of access. Data Flow Diagrams Data Flow Diagrams are a widely used technique for representing the information flows of a system. They are a particular feature of SSADM methodology (Structured Systems Analysis and Design Method). They arc used in the early stages of a systems analysis to provide an understanding of the present system. As the project proceeds they are used to represent the required and also as a basis for program specification. DFDs can be drawn at various levels of detail. At the high Level the DFD is known as a Context Diagram which shows the system as one box with flows going to and coming from external entities. This can then be decomposed into more detailed DFDs. A DFD can show the physical processing of the present system detailing the departments and individuals concerned in the work, or it can be a logical DFD which shows what happens to the data rather than how the processing is carried out. A logical DFD is useful as it frees the analyst from being over influenced by the present system. Purpose of A Data flow diagram It is a diagrammatic representation of information flows within a system showing: * how information enters and leaves the system. * what changes the information. * where information is stored. A DFD is also useful to: * show the boundaries and scope of the system. * check the completeness of the analyses * ensure that all information flows and activities have been considered. * show the major functional areas of the system and therefore identify particular program requirements. DFDs can he used by both technical and non-technical staff and is used in discussions between the analyst and the user. One of the greatest strengths of DFDs is that they can be used to describe a system at several levels. Components of DFDs External Entity The source of information provided to the system. Or the recipient of information provided by the system. An oval shape represents it. If understanding of the DFD can be enhanced then an external entity may be drawn more than once. Process A process transforms or manipulates data within the system. It is represented by a box and will include a numeric identifier, the location of the process, and the process identifier. When naming processes begin with a verb and follow it by an object. e.g. Make Delivery, Receive payment. The object should always be singular. Data Store Data stores may be manual or computer files, and represent the place where a process places data so that it can be retrieved later. Each data store is labelled with the letter M for manual or D for computer and is given a number. Data Flow Represented by an arrow which should be labelled with the data that is being carried (never use a verb on a data flow). Boundary A boundary is sometimes drawn around a DFD to show the limits of what is being investigated. Levels of DFD Level 0 DFD (Context Diagram) Shows the entire system a single black box communicating with the external entities. Level 1 DFD An outline DFD using typically up to 12 process boxes. It shows: * system boundaries, * external entities * main system flows, * main system functions. * data stores. Level 2 and 3 DFD Successively more detailed DFDs showing up to 8 process boxes per DFD. Data Flow Diagrams How do you start? Case study Example Draw a Data flow diagram of the following scenario Data flow diagrams A manufacturing company has a strict health and safety policy. They have a small health and safety department, which maintains safety levels in the organisation. They require that employees report any problems to them if they discover faults within the organisation of a hazardous or potentially hazardous nature. Reports from employees are received in the Health and Safety department either by telephone, e-rnail or internal memo. This information is received by the health and safety administrator who logs the calls on his fault logging computer database. The computer database issues a unique problem number, which is given to the head of department of the employee highlighting the fault. The head of department is also provided with details of the nature of the problem. There are two health and safety inspectors employed by the organisation who investigate the problems when they occur. They are based in the health and safety department and are given the details of the problem and the fault number from the computer database by the administrator who logs the assignment of the task on the fault logging database. When the problem is investigated and therefore the task is completed the inspectors contact the administrator to advise them of the situation. The administrator advises the particular head of department that the necessary work has been carded out and the task is closed in the fault logging database. 1. Pick out relevant information and place in tabular form External entity Processes Data stores Data. flows employee report problem fault logging fault details head of dept collect problem ID No health and safety inspectors close problem Fault No assignment details Completed details Fault closed details Health and Safety Department Fault Reporting System 2. Context Diagram (no data stores) 3. Produce the Data Flow diagram Example 1 A purchasing department receives a purchase requisition from the stores. The requisition is checked, and an invalid requisition is returned to the stores for correction. An order is made out using a file of approved suppliers, and sent to the appropriate supplier. A copy order is filed. The requisition is filed. When the goods arc received the invoice is compared with the filed copy order and an invalid invoice is returned to the supplier. Valid invoices are passed to the accounts department for payment, and fulfilled orders are filed. Draw a Level 0 and level 1 DFD for the purchase requisition system. Example 2 When an invoice is received from a supplier, it is checked against a file of authorised purchases. If the invoice does not much an authorised purchase it is returned to the supplier with, a querying letter. If the invoice matches an authorised purchase, but is for an incorrect amount then it is returned to the supplier with a standard form. If the invoice reconciles, a payment authorisation is made out. A cheque is then sent to the supplier, and the invoice and the authorisation are filed. Draw a level 0 and Level 1 DFD for the system. Example 3 This case study is based on the video issue recording system of the Gentlepeoples Video Library Club (GVLC). GVLC specialises in obscure videos that are not readily available from other sources. GVLC lends only to members of the Video Society part of the exclusive and very desirable Gentlepeoples Club. Details of finance are outside the scope of the investigation. Any member of the club is automatically a member of the library. Club membership is for one year; a few new members are admitted on 1 January each year; new members are not admitted during the year. The library is set up along conventional lines, though members are not restricted as to the number of videos they may borrow at any one time. Videos are requested for return only if required by another member. Most active users of the library regularly change their videos. Two or three copies of popular titles are available. In order to borrow a video a member selects it takes it to the issue desk and gives the video and his club membership card to the librarian. The librarian takes the video ID card from the video sleeve and adds the membership number to the card. The librarian places the card in the loans file and the member leaves with the video. When a member returns a video. He or she presents the video to the librarian. The librarian finds the video card in the loans file and places the card in the video sleeve before returning the video to the library shelves. To reserve a video, which is on, can. A member asks the librarian and leaves their membership number. The Librarian finds a relevant video in the loans file and adds the members number on the reservation column on the video card. The librarian also makes a note of the member who has the video on loan and completes a return request card addressed to that member. The address is taken from the library copy of the club membership book. When the reserved video is returned the librarian puts the video under the counter and completes a Reservation Ready card addressed to the member who requested the reservation again taking the address from the membership book. Tine member requiring he video can then pick the video up from the librarian and have it issued in the usual manner. Members make many enquiries of the librarians: typical questions include is the video entitled Dziadek on loan? Which video did actress Anna Kucharski appear in? have we a video entitled Son of Arturo? Have we any videos on the subject Right Action? The librarians are able to answer these queries by inspecting the loans file the actor index the subject index and the title index. In addition to the above duties the librarians receive new videos from the social committee of the club. The selection ordering and payment for the videos is outside the scope of this investigation. On receipt of the new video the librarian has to make out a video card for insertion in the video sleeve and the relevant entries for the indexes. The librarians are also responsible for amending the library copy of the membership book with changes of address and at the end of the year far collecting the new membership bock from the Club Secretary. Answers Example 3 GLVC Video Library Context Diagram Level 1 DFD Activity 1 College Library 1. Zero Normal Form 0NF List Attributes Stud# Name Address TG Tutor Book# Title ISBN ReturnDate Identify Primary key and repeating attributes. Write out in 0NF using standard notation:- When an entity has has a Repeating Attribute (e.g book has several authors) The repeating attribute is shown with a line over it STUDENT(Stud#, Name, Address, TG, Tutor, Book#, Title, ISBN, ReturnDate) 2. First Normal Form -1NF Rule- An entity in First Normal Form must not contain any repeating attributes. Remove repeated attributes to form a new entity LOAN_BOOK. There are now 2 entities in 1NF:- STUDENT(Stud#, Name, Address, TG, Tutor,) LOAN_BOOK(Book#,Stud#, Title, ISBN, ReturnDate) (A composite key is required to uniquely identify each loan of a particular book) 3. Second Normal Form 2NF Rule An entity is in 2NF if it is 1NF and all non key attributes are fully functionally dependent on the whole of the primary key. ( 2NF applies to entities with composite keys, that is a primary key composed of two or more attibutes. An entity which is already in 1NF, with a single attribute primary key is automatically in at least 2NF) The STUDENT entity has a single attribute primary key and is therefore already in 2NF. The LOAN_BOOK entity has a composite primary key so we need to examine all the non-key attributes to ensure they are fully functionally dependent on the whole of the primary key. Non-key attribute Dependent on:- Title Book# ISBN Book# ReturnDate Book#, Stud# Therefore Title and ISBN need to be removed to form a new entity BOOK. Book# is included to provide a link. The tables in 2NF are now:- STUDENT(Stud#, Name, Address, TG, Tutor,) LOAN_BOOK(Book#,Stud#, ReturnDate) BOOK(Book#, Title, ISBN) 4. Third Normal Form 3NF Rule To be in 3NF an entity must be in 2 NF (and therefore in 1NF) and contain no non-key dependencies. Fields which are not part of the primary key must always depend on the primary key and not on anything else, such as another non key field. Consider the entity STUDENT, Name Address depend on the primary key but Tutor depends on the Tutor Group code TG and not on Stud#. They should therefore be removed to form a new entity, TUTOR. A copy of the code TG is left in the student table to form a link. STUDENT(Stud#, Name, Address, TG) TUTOR(TG, Tutor) Consider the entity LOAN_BOOK, return date is dependent on the primary key and therefore already in 3NF. Consider the entity BOOK, title is dependent on the ISBN and not on the Book#, this should be removed to create a new entity ISBN. A copy of ISBN is left in the BOOK entity to provide a link. BOOK(Book#, ISBN) ISBN(ISBN, Title) The final tables are:- STUDENT(Stud#, Name, Address, TG) TUTOR(TG, Tutor) LOAN_BOOK(Book#,Stud#, ReturnDate) BOOK(Book#, ISBN) ISBN(ISBN, Title) H. T. Harvey 6-Feb-03 1 of 18 Chapter 18