Chapter 4 Database System Development Lifecycle Pearson Education 2009 2 2 Chapter 4 - Objectives u Main components of an information system. u Main stages of database system development lifecycle. u Main phases of database design: conceptual, logical, and physical design. u Benefits of CASE tools. Pearson Education 2009 3 2 Chapter 4- Objectives u How to evaluate and select a DBMS. Distinction between data administration and database administration. u Purpose and tasks associated with data administration and database administration. Pearson Education 2009 4 Software Depression u Last 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. u Effort spent on maintenance began to absorb resources at an alarming rate. Pearson Education 2009 5 Software Depression u As a result, many major software projects were late, over budget, unreliable, difficult to maintain, performed poorly. u In late 1960s, led to software crisis, now refer to as the software depression. Pearson Education 2009 6 Software Depression u Major 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. u Structured approach to development was proposed called Information Systems Lifecycle (ISLC) / Software Development Lifecycle (SDLC) u Develop database system Database System Lifecycle (DBLC) Pearson Education 2009 7 Information Systems Lifecycle: Information System Resources that enable collection, management, control, and dissemination of information throughout an organization. u Computer-based information system includes Database, database software, application software, computer hardware and people/personnel. u Database is fundamental component of IS, and its development/usage should be viewed from perspective of the wider requirements of the organization. u Lifecycle of an organizations IS lifecycle of the database system Pearson Education 2009 8 Database System Development Lifecycle u Database planning u System definition u Requirements collection and analysis u Database design u DBMS selection (optional) Pearson Education 2009 9 Database System Development Lifecycle u Application design u Prototyping (optional) u Implementation u Data conversion and loading u Testing u Operational maintenance Pearson Education 2009 10 Stages of the Database System Development Lifecycle Pearson Education 2009 11 Database Planning u Management activities that allow stages of database system development lifecycle to be realized as efficiently and effectively as possible. u Must be integrated with overall IS strategy of the organization. Pearson Education 2009 12 Database Planning u THREE main issues involved in formulating an IS strategy: Identification of enterprise plans and goals & determine IS needs Evaluation of current IS IT opportunities that might yield competitive advantage. u Steps: Define the Mission Statement Identifying the Mission Objectives Pearson Education 2009 13 Database Planning Mission Statement u Mission statement for the database project defines major aims of database application. u Those driving database project normally define the mission statement. u Mission statement helps clarify purpose of the database project and provides clearer path towards the efficient and effective creation of required database system. Pearson Education 2009 14 Database Planning Mission Objectives u Once mission statement is defined, mission objectives are defined. u Each objective should identify a particular task that the database must support. u 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. Pearson Education 2009 15 Database Planning Mission Statement & Objectives EXAMPLE: ShowInfo Mission Statement u The purpose of ShowInfo is to maintain show information, allow users to indicate their presence at a show and view those attending, and to facitilitate sharing of concert experiences after the show. ShowInfo Mission Objectives u ShowInfo must maintain data pertinent to attending concerts. u ShowInfo must allow users to indicate shows that they will/might attend, as well as shows that they have attended in the past. u ShowInfo must allow users to maintain setl ist and concert photo data. u ShowInfo must create reports of future shows. u ShowInfo must archive data about previous shows. Pearson Education 2009 16 Database Planning u Database 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, how design and implementation should proceed. Pearson Education 2009 17 System Definition Describes scope and boundaries of database system and the major user views. u Included within the scope and boundary of the database system are the major user views that are to be supported by the database Pearson Education 2009 18 System Definition: User Views u Defines what is required of a database system from perspective of: a particular job role (such as Manager or Supervisor) or enterprise application area (such as marketing, personnel, or stock control). Pearson Education 2009 19 System Definition: User Views u Database application may have one or more user views. u Identifying user views helps ensure that no major users of the database are forgotten when developing requirements for new system. u User views also help in development of complex database system allowing requirements to be broken down into manageable pieces. Pearson Education 2009 20 System Definition: User Views u Defines what is required of a database system Data to be held Transactions to be performed on the data u Requirements of a user view Distinct to that view Overlap with other views Pearson Education 2009 21 Representation of a Database System with Multiple User Views Pearson Education 2009 22 Requirements Collection and Analysis u Process of collecting and analyzing information about the part of organization to be supported by the database system, and using this information to identify users requirements of new system. u Involves the collection and analysis of information part of enterprise to be served by the database Pearson Education 2009 23 Requirements Collection and Analysis u 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; any additional requirements for new database system. u Information is analyzed to identify requirements to be included in new database system. u Described in the requirements specification. (documents) u Preliminary stage to database design Pearson Education 2009 24 Requirements Collection and Analysis u Amount of data gathered: Nature of the problem Policies of the enterprise u Information collected convert to more structured statement of requirements u Use: Requirements Specification Techniques Structured Analysis and Design (SAD) Data Flow Diagram (DFD) Hierarchical Input Process Output (HIPO) Pearson Education 2009 25 Requirements Collection and Analysis u Another important activity is deciding how to manage the requirements for a database system with multiple user views. u Three main approaches: centralized approach; view integration approach; combination of both approaches. Pearson Education 2009 26 Requirements Collection and Analysis: Multiple User Views u Centralized/One-Shot approach Requirements for each user view are merged into a single set of requirements. A data model is created representing all user views during the database design stage. Preferred when there is significant overlap in requirements for each user view Pearson Education 2009 27 Centralized Approach to Managing Multiple User Views Pearson Education 2009 28 Requirements Collection and Analysis: Multiple User Views u View integration approach Requirements for each user view remain as separate lists. Data models representing each user view are created and then merged later during the database design stage. Pearson Education 2009 29 Requirements Collection and Analysis: Multiple User Views u Data model representing single user view (or a subset of all user views) is called a local data model. u Each model includes diagrams and documentation describing requirements for one or more but not all user views of database. Pearson Education 2009 30 Requirements Collection and Analysis: Multiple User Views u Local data models are then merged at a later stage during database design to produce a global data model, which represents all user views for the database. u Preferred: significant differences between user views Pearson Education 2009 31 View Integration Approach to Managing Multiple User Views Pearson Education 2009 32 Requirements Collection and Analysis: Multiple User Views u Combination : Use both centralized & view integration approaches Example: Requirements for two or more user views: merged using centralized approach local logical data model The local logical data model merged with other model using view integration approach global logical data model Pearson Education 2009 33 Database Design u Process of creating a design for a database that will support the enterprises mission statement and mission objectives for the required database system. Pearson Education 2009 34 Database Design: Approaches u Main approaches include: Top-down Bottom-up Inside-out Mixed Pearson Education 2009 35 Database Design u Top-down Suitable for complex databases Starts with development of data models ER model Identify entities relationship attributes Pearson Education 2009 36 Database Design u Bottom-up Begins at the fundamental level of attributes Associations between attributes are grouped into relations that represent types of entities and relationship between entities Appropriate for simple databases with small number of attributes Pearson Education 2009 37 Database Design u Inside-out Related to bottom-up Identify major entities consider other entities, r/ships & attributes u Mixed Uses both bottom-up & top-down approach for various parts of the model Final combine all parts Pearson Education 2009 38 Database Design: Data Modeling u Main purposes of data modeling include: to assist in understanding the meaning (semantics) of the data; to facilitate communication about the information requirements. u Building data model requires answering questions about entities, relationships, and attributes. Pearson Education 2009 39 Database Design u A data model ensures we understand: each users perspective of the data; nature of the data itself, independent of its physical representations use of data across user views. u Can be used to convey the designers understanding of the information requirements of the enterprise u Support communication between users and designers u ER model Pearson Education 2009 40 Criteria to Produce an Optimal Data Model Pearson Education 2009 41 Database Design u Three phases of database design: Conceptual database design Logical database design Physical database design. Pearson Education 2009 42 Conceptual Database Design u Process of constructing a model of the data used in an enterprise, independent of all physical considerations. u Data model is built using the information in users requirements specification. u Throughout the process: model is tested and validated against the users requirements. u Conceptual data model is source of information for logical design phase. Pearson Education 2009 43 Logical Database Design u Process of constructing a model of the data used in an enterprise based on a specific data model (e.g. relational), but independent of a particular DBMS and other physical considerations. u Conceptual data model is refined and mapped on to a logical data model. u Logical data model: based on the target data model for the database (relational data model, object oriented, etc) Pearson Education 2009 44 Logical Database Design u Model tested and validated against the users requirements Normalization: test the correctness of a logical data model Ensures the relations derived from data model do not display data redundancy Model should also be examined to ensure it supports the transactions specified by the users u Logical data model: source of information for physical database design Pearson Education 2009 45 Physical Database Design u Process of producing a description of the database implementation on secondary storage. u Describes base relations, file organizations, and indexes used to achieve efficient access to data. u Also describes any associated integrity constraints and security measures. u Tailored to a specific DBMS system: First identify the target DBMS Pearson Education 2009 46 Physical Database Design u In general: describe HOW we intend to implement the logical database design. u For relational model: Create set of relational tables and constraints on these tables from the information presented in logical data model Identify specific storage structures and access methods for the data to achieve optimum performance for the database system Design security protection Pearson Education 2009 47 Three-Level ANSI-SPARC Architecture and Phases of Database Design Pearson Education 2009 48 DBMS Selection u Selection of an appropriate DBMS to support the database system. u Undertaken at any time prior to logical design provided sufficient information is available regarding system requirements. u Select a system that meets the current and future requirements of the enterprise, balance against costs. Pearson Education 2009 49 DBMS Selection u Main steps to selecting a DBMS: define Terms of Reference of study State the objectives and scope of the study and tasks need to be undertaken Description of the criteria to be used to evaluate the DBMS Preliminary list of possible products Constraints & timescales for the study shortlist two or three products evaluate products recommend selection and produce report Pearson Education 2009 50 DBMS Evaluation Features Pearson Education 2009 51 DBMS Evaluation Features Pearson Education 2009 52 Example - Evaluation of DBMS Product Pearson Education 2009 53 Application Design u Design of user interface and application programs that use and process the database. u Database design and application design are parallel activities. u Includes two important activities: transaction design; user interface design. Pearson Education 2009 54 Application Design - Transactions u An action, or series of actions, carried out by a single user or application program, which accesses or changes content of the database. u Should define and document the high-level characteristics of the transactions required. Pearson Education 2009 55 Application Design - Transactions u 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. u Three main types of transactions: retrieval, update, and mixed. Pearson Education 2009 56 Prototyping u Building working model of a database system. u Purpose 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. Pearson Education 2009 57 Prototyping u Requirements prototyping Use prototype to determine requirements Requirements complete prototype discarded u Evolutionary prototyping Same purpose Prototype not discarded further development becomes working database system Pearson Education 2009 58 Implementation u Physical realization of the database and application designs. Use DDL to create database schemas and empty database files. Use DDL to create any specified user views. Use 3GL or 4GL to create the application programs. This will include the database transactions implemented using the DML, possibly embedded in a host programming language. Pearson Education 2009 59 Data Conversion and Loading u Transferring any existing data into new database and converting any existing applications to run on new database. u Only required when new database system is replacing an old system. DBMS normally has utility that loads existing files into new database. u May be possible to convert and use application programs from old system for use by new system. Pearson Education 2009 60 Testing u Process of running the database system with the intent of finding errors. u Use carefully planned test strategies and realistic data. u Testing cannot show absence of faults; it can show only that software faults are present. u Demonstrates that database and application programs appear to be working according to requirements. Pearson Education 2009 61 Testing u Should also test usability of system. u Evaluation conducted against a usability specification. u Examples of criteria include: Learnability how long does it take a new user to become productive with the system? Performance How well does the system response match the users work practice? Robustness How tolerant is the system of user error? Pearson Education 2009 62 Testing Recoverability How good is the system at recovering from user errors? Adaptability How closely is the system tied to a single model of work? Pearson Education 2009 63 Operational Maintenance u Process of monitoring and maintaining database system following installation. u Monitoring performance of system. if performance falls, may require tuning or reorganization of the database. u Maintaining and upgrading database application (when required). u Incorporating new requirements into database application. Pearson Education 2009 64 CASE (Computer Aided Software Engineering) Tools Support provided by CASE tools include: - data dictionary to store information about database systems data; - design tools to support data analysis; - tools to permit development of corporate data model, and conceptual and logical data models; - tools to enable prototyping of applications. Pearson Education 2009 65 CASE Tools u Provide following benefits: Standards - enforce standards Integration store all information generated in repository; possible to store all data stages of DBLC Support for standard methods simplify the process of structured techniques documentation correct, more current Consistency all information in the data dictionary interrelated CASE tools can check its consistency Automation - automatically transform parts of a design spec into executable codes Pearson Education 2009 66 CASE Tools and Database System Development Lifecycle Pearson Education 2009 67 Data Administration and Database Administration u The Data Administrator (DA) and Database Administrator (DBA) are responsible for managing and controlling the corporate data and corporate database, respectively. u DA is more concerned with early stages of database system development lifecycle and DBA is more concerned with later stages. Pearson Education 2009 68 Data Administration u Management of data resource including: database planning, development and maintenance of standards, policies and procedures, and conceptual and logical database design. Pearson Education 2009 69 Database Administration u Management of physical realization of a database system including: physical database design and implementation, setting security and integrity controls, monitoring system performance, and reorganizing the database. Pearson Education 2009