2 Chapter NameSeptember 98Lecture’s ObjectivesPut all the previous lectures into context (Conceptual and Logical Design, Normalisation and SQL).Learn the main stages of database application development.Use these stages as guidelines for your MSc project (if you choose to undertake a project which involves developing a Database System).22
3 Software DepressionLast few decades have seen proliferation of software applications, many requiring constant maintenance involving:correcting faults,implementing new user requirements,modifying software to run on new or upgraded platforms.Effort spent on maintenance began to absorb resources at an alarming rate.
4 Software Depression As a result, many major software projects were late,over budget,unreliable,difficult to maintain,performed poorly.This led to ‘software crisis’, now referred to as the ‘software depression’.
5 Software DepressionMajor reasons for failure of software projects includes:- lack of a complete requirements specification;- lack of appropriate development methodology;- poor decomposition of design into manageable components.Structured approach to development was proposed called information systems lifecycle.
6 Information SystemResources that enable collection, management, control, and dissemination of information throughout an organization.Database is fundamental component of I.S., and its development/usage should be viewed from perspective of the wider requirements of the organization.
7 Database Application Lifecycle Database planningSystem definitionRequirements collection and analysisDatabase designDBMS selectionApplication designPrototypingImplementationData conversion and loadingTestingOperational maintenance.
9 Database PlanningManagement activities that allow stages of database application lifecycle to be realised as efficiently and effectively as possible.Must be integrated with overall IS strategy of the organization.
10 Database Planning – Mission Statement Mission statement for the database project defines major aims of database application.Those driving database project normally define the mission statement.Mission statement helps clarify purpose of the database project and provides clearer path towards the efficient and effective creation of required database application.
11 Database Planning – Mission Objectives Once mission statement is defined, mission objectives are defined.Each objective should identify a particular task that the database must support.May be accompanied by some additional information that specifies the work to be done, the resources with which to do it, and the money to pay for it all.
12 Database PlanningDatabase planning should also include development of standards that govern:how data will be collected,how the format should be specified,what necessary documentation will be needed
13 System DefinitionDescribes scope and boundaries of database application and the major user views.User view defines what is required of a database application from perspective of:a particular job role (such as Manager or Supervisor) orenterprise application area (such as marketing, personnel, or stock control).
14 Representation of a Database Application with Multiple User Views
15 Requirements Collection and Analysis Process of collecting and analyzing information about the part of organization to be supported by the database application, and using this information to identify users’ requirements of new system.
16 Requirements Collection and Analysis Information is gathered for each major user view including:a description of data used or generated;details of how data is to be used/generated;
17 Requirements Collection and Analysis Data model representing single user view is called a local data model, composed of diagrams and documentation describing requirements of a particular user view of database.Local data models are then merged to produce a global data model, which represents all user views for the database.
18 Database DesignProcess of creating a design for a database that will support the enterprise’s operations and objectives.
19 Database Design Major aims: Represent data and relationships between data required by all major application areas and user groups.Provide data model that supports any transactions required on the data.Specify a minimal design that is appropriately structured to achieve stated performance requirements for the system (such as response times).
20 Database Design Three phases of database design: Conceptual database designLogical database designPhysical database design.
21 Conceptual Database Design Process of constructing a model of the information used in an enterprise, independent of all physical considerations.Data model is built using the information in users’ requirements specification.Source of information for logical design phase.Use of ER Diagrams / UML Diagrams…
22 Logical Database Design Process of constructing a model of the information used in an enterprise based on a specific data model (e.g. relational), but independent of a particular DBMS and other physical considerations.Conceptual data model is refined and mapped on to a logical data model.For example, design of Tables if relational model is used.
23 Physical Database Design Process of producing a description of the database implementation on secondary storage.Describes storage structures and access methods used to achieve efficient access to data (Files, indexes…).Tailored to a specific DBMS.
24 DBMS SelectionSelection of an appropriate DBMS to support the database application.Undertaken at any time prior to logical design provided sufficient information is available regarding system requirements.Main steps to selecting a DBMS:define Terms of Reference of study;shortlist two or three products;evaluate products;recommend selection and produce report.
27 Application DesignDesign of user interface and application programs that use and process the database.Database and application design are parallel activities.Includes two important activities:transaction design (e.g., Queries);user interface design (e.g., Forms).
28 Application Design - Transactions Important characteristics of transactions:data to be used by the transaction;functional characteristics of the transaction;output of the transaction;importance to the users;expected rate of usage.Three main types of transactions: retrieval, update, and mixed.
29 Application Design – User Interface Guidelines for form/report design:Meaningful titleComprehensible instructionsLogical grouping and sequencing fieldsVisually appealing layout of the form/reportFamiliar field labelsConsistent use of colourVisible space and boundaries for data-entry fieldsConvenient cursor movementError messages for unacceptable valuesOptional fields marked clearlyExplanatory messages for fieldsCompletion signal
30 Prototyping Purpose Building working model of a database application. to identify features of a system that work well, or are inadequate;to suggest improvements or even new features;to clarify the users’ requirements;to evaluate feasibility of a particular system design.
31 Data Conversion and Loading Transferring any existing data into new database and converting any existing applications to run on new database.Only required when new database system is replacing an old system.DBMS normally has utility that loads existing files into new database.May be possible to convert and use application programs from old system for use by new system.
32 TestingProcess of executing application programs with intent of finding errors.Use carefully planned test strategies and realistic data.Testing cannot show absence of faults; it can only demonstrate that database and application programs appear to be working according to requirements.
33 Operational Maintenance Process of monitoring and maintaining system following installation.Monitoring performance of system.if performance falls, may require tuning or reorganization of the database.Maintaining and upgrading database application (when required).Incorporating new requirements into database application.
34 Data Administration and Database Administration Data Administration: Management of data resource including:database planning,development and maintenance of standards, policies and procedures, and conceptual and logical database design.Database Administration: Management of physical realisation of a database application including:physical database design and implementation,setting security and integrity controls,monitoring system performance, and reorganising the database.
36 Fact-Finding Techniques Formal process of using techniques such as interviews and questionnaires to collect facts about systems, requirements, and preferences.
37 Fact-Finding Techniques Database developer normally uses several fact-finding techniques during a single database project including:examining documentation,interviewing,observing organisation in operation,research,questionnaires.
38 Examining Documentation Can be useful:to gain some insight as to how the need for a database arose;to identify the part of the organisation associated with the problem;to understand the current system.
39 InterviewingMost commonly used, and normally most useful fact-finding technique.Objectives include finding out facts, verifying facts, clarifying facts, generating enthusiasm, getting end-user involved, identifying requirements, and gathering ideas and opinions.Open-ended questions allow interviewee to respond in any way that seems appropriate.Closed-ended questions restrict answers to either specific choices or short, direct responses.
40 Observing the Organisation in Operation Effective technique for understanding system.Possible to participate in, or watch, a person perform activities to learn about system.Useful when validity of data collected is in question or when complexity of certain aspects of system prevents clear explanation by end-users.
41 Research Useful to research application and problem. Use computer trade journals, reference books, and Internet (including user groups and bulletin boards).Provide information on how others have solved similar problems, plus whether or not software packages exist to solve, or even partially solve, the problem.
42 QuestionnairesConduct surveys through questionnaires – special-purpose documents that allow facts to be gathered from a large number of people while maintaining some control over their responses.Two types of questions, namely free-format and fixed-format.
44 Overview of the Case Study DreamHome is a company that specialises in property renting, by taking an intermediate role between property owners and clients who require to rent a property.DreamHome operates several branches throughout the UK. Each branch has a number of staff including a Manager, Supervisors, and Assistants. Each branch offers a range of properties for rent.The Director of the company feels that a database could help in avoiding the many mistakes occurring in the current paper-based operations of the company.
45 DreamHome – Database Planning - Defining the mission statement for the database system Typical questions we might ask the Director:“What is the purpose of your company?”“Why do you feel that you need a database?”Example of a mission statement: “The purpose of the database system is to maintain the data that is used and generated to support the property rentals business for our clients and property owners and to facilitate the cooperation and sharing of information between branches”.
46 DreamHome – Database Planning - Identifying the objectives for the database system Typical questions to various members of staff include:“What is your job description?”“What kinds of tasks do you perform in a typical day?”“What kinds of data/reports do you use?”Examples of objectives:To maintain (enter, update, and delete) data on branchesTo perform searches on branchesTo report on branches…
47 DreamHome – System Definition – Defining the system’s boundary PropertyAdvertisingRentalsCustomerServicesStaffHumanResourcesPayrollMarketingSalesSystem’s Boundary
48 DreamHome – System Definition - Identifying the major user views DataAccess TypeDirectorManagerSupervisorAssistantAll BranchesMaintainQueryXReportSingle BranchAll StaffBranch Staff… etc
49 DreamHome – Requirements Collection & Analysis – Users’ Requirements Specification Data Requirements:Branches: The data held on each branch office includes a unique branch number, address (street, city, and postcode)…Staff: The data stored on each member of staff includes staff number, name……
50 Transaction Requirements: DreamHome – Requirements Collection & Analysis – Users’ Requirements SpecificationTransaction Requirements:Data entry:Enter the details of a new branch…Data update/deletion:Update/delete the details of a member of staff at a branch…Data queries:List the names of staff supervised by a named supervisor…
51 DreamHome – Requirements Collection & Analysis – System’s Specification The types of features described in the system’s specification include:Initial database sizeDatabase rate of growthThe types and average number of record searchesNetworking and shared access requirementsPerformanceSecurityBackup and recoveryLegal issues
52 DreamHome – Requirements Collection & Analysis – System’s Specification Initial database size:There are approximately 2000 members of staff at 100 branches. There is an average of 20 and a maximum of 40 members at each branch…Database rate of growth:Approximately 500 new properties and 200 new owners are added to the database each month…Types and average number of record search:Searching for the details of a branch – approximately 10 per day…Networking and shared access requirements:All branches should be networked to a centralised database at the main office. The system should allow for at least three people concurrently accessing the system for each branch…
53 DreamHome – Requirements Collection & Analysis – System’s Specification Performance:During non-peak periods expect less than 1 second response time for all single record searches…Security:The database should be password protected…Backup and Recovery:The database should be backed up daily at 12 midnight.Legal issues:Implement UK’s law on the computerised storage of personal data (staff, clients and owners).
54 Further ReadingSee “Database Systems”, Connolly & Begg, for full case study, including conceptual and logical design.