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Chapter: Fundamentals of Database Systems : Conceptual Modeling and Database Design : Practical Database Design Methodology and Use of UML Diagrams

The Role of Information Systems in Organizations

1. The Organizational Context for Using Database Systems 2. The Information System Life Cycle 3. The Database Application System Life Cycle

The Role of Information Systems in Organizations


1. The Organizational Context for Using Database Systems


Database systems have become a part of the information systems of many organizations. Historically, information systems were dominated by file systems in the 1960s, but since the early 1970s organizations have gradually moved to database management systems (DBMSs). To accommodate DBMSs, many organizations have created the position of database administrator (DBA) and database administration departments to oversee and control database life-cycle activities. Similarly, information technology (IT) and information resource management (IRM) departments have been recognized by large organizations as being key to successful business management for the following reasons:


        Data is regarded as a corporate resource, and its management and control is considered central to the effective working of the organization.


        More functions in organizations are computerized, increasing the need to keep large volumes of data available in an up-to-the-minute current state.


        As the complexity of the data and applications grows, complex relationships among the data need to be modeled and maintained.


        There is a tendency toward consolidation of information resources in many organizations.


        Many organizations are reducing their personnel costs by letting end users perform business transactions. This is evident with travel services, financial services, higher education, government, and many other types of services. This trend was realized early on by online retail goods outlets and customer-to-business electronic commerce, such as Amazon.com and eBay. In these organizations, a publicly accessible and updatable operational database must be designed and made available for the customer transactions.


Many capabilities provided by database systems have made them integral compo-nents in computer-based information systems. The following are some of the key features that they offer:


        Integrating data across multiple applications into a single database.


        Support for developing new applications in a short time by using high-level languages like SQL.


        Providing support for casual access for browsing and querying by managers while supporting major production-level transaction processing for customers.


From the early 1970s through the mid-1980s, the move was toward creating large centralized repositories of data managed by a single centralized DBMS. Since then, the trend has been toward utilizing distributed systems because of the following developments:


Personal computers and database system-like software products such as Excel, Visual FoxPro, Access (Microsoft), and SQL Anywhere (Sybase), and public domain products such as MySQL and PostgreSQL, are being heavily utilized by users who previously belonged to the category of casual and occasional database users. Many administrators, secretaries, engineers, scientists, architects, and students belong to this category. As a result, the practice of creating personal databases is gaining popularity. It is sometimes possible to check out a copy of part of a large database from a mainframe computer or a database server, work on it from a personal workstation, and then restore it on the mainframe. Similarly, users can design and create their own databases and then merge them into a larger one.

        The advent of distributed and client-server DBMSs (see Chapter 25) is open-ing up the option of distributing the database over multiple computer systems for better local control and faster local processing. At the same time, local users can access remote data using the facilities provided by the DBMS as a client, or through the Web. Application development tools such as PowerBuilder and PowerDesigner (Sybase) and OracleDesigner and Oracle Developer Suite (Oracle) are being used with built-in facilities to link appli-cations to multiple back-end database servers.


        Many organizations now use data dictionary systems or information repositories, which are mini DBMSs that manage meta-data—that is, data that describes the database structure, constraints, applications, authoriza-tions, users, and so on. These are often used as an integral tool for informa-tion resource management. A useful data dictionary system should store and manage the following types of information:


                                                          Descriptions of the schemas of the database system.


                                                          Detailed information on physical database design, such as storage struc-tures, access paths, and file and record sizes.


                                                          Descriptions of the types of database users, their responsibilities, and their access rights.


                                                          High-level descriptions of the database transactions and applications and of the relationships of users to transactions.


                                                          The relationship between database transactions and the data items refer-enced by them. This is useful in determining which transactions are affected when certain data definitions are changed.


                                                          Usage statistics such as frequencies of queries and transactions and access counts to different portions of the database.


                                                          The history of any changes made to the database and applications, and documentation that describes the reasons for these changes. This is some-times referred to as data provenance.


This meta-data is available to DBAs, designers, and authorized users as online sys-tem documentation. This improves the control of DBAs over the information sys-tem as well as the users’ understanding and use of the system. The advent of data warehousing technology (see Chapter 29) has highlighted the importance of meta-data.


When designing high-performance transaction processing systems, which require around-the-clock nonstop operation, performance becomes critical. These data-bases are often accessed by hundreds, or thousands, of transactions per minute from remote computers and local terminals. Transaction performance, in terms of the average number of transactions per minute and the average and maximum transac-tion response time, is critical. A careful physical database design that meets the organization’s transaction processing needs is a must in such systems.


Some organizations have committed their information resource management to certain DBMS and data dictionary products. Their investment in the design and implementation of large and complex systems makes it difficult for them to change to newer DBMS products, which means that the organizations become locked in to their current DBMS system. With regard to such large and complex databases, we cannot overemphasize the importance of a careful design that takes into account the need for possible system modifications—called tuning—to respond to changing requirements. We will discuss tuning in conjunction with query optimization in Chapter 21. The cost can be very high if a large and complex system cannot evolve, and it becomes necessary to migrate to other DBMS products and redesign the whole system.



2. The Information System Life Cycle


In a large organization, the database system is typically part of an information sys-tem (IS), which includes all resources that are involved in the collection, manage-ment, use, and dissemination of the information resources of the organization. In a computerized environment, these resources include the data itself, the DBMS soft-ware, the computer system hardware and storage media, the personnel who use and manage the data (DBA, end users, and so on), the application programs (software) that accesses and updates the data, and the application programmers who develop these applications. Thus the database system is part of a much larger organizational information system.


In this section we examine the typical life cycle of an information system and how the database system fits into this life cycle. The information system life cycle has been called the macro life cycle, whereas the database system life cycle has been referred to as the micro life cycle. The distinction between them is becoming less pronounced for information systems where databases are a major integral compo-nent. The macro life cycle typically includes the following phases:


        Feasibility analysis. This phase is concerned with analyzing potential appli-cation areas, identifying the economics of information gathering and dissemination, performing preliminary cost-benefit studies, determining the complexity of data and processes, and setting up priorities among applications.


        Requirements collection and analysis. Detailed requirements are collected by interacting with potential users and user groups to identify their particu-lar problems and needs. Interapplication dependencies, communication, and reporting procedures are identified.


        Design. This phase has two aspects: the design of the database system and the design of the application systems (programs) that use and process the database through retrievals and updates.


        Implementation. The information system is implemented, the database is loaded, and the database transactions are implemented and tested.


Validation and acceptance testing. The acceptability of the system in meeting users’ requirements and performance criteria is validated. The system is tested against performance criteria and behavior specifications.

        Deployment, operation, and maintenance. This may be preceded by con-version of users from an older system as well as by user training. The operational phase starts when all system functions are operational and have been validated. As new requirements or applications crop up, they pass through the previous phases until they are validated and incorporated into the system. Monitoring of system performance and system maintenance are important activities during the operational phase.


3. The Database Application System Life Cycle


Activities related to the micro life cycle, which focuses on the database application system, include the following:


        System definition. The scope of the database system, its users, and its applications are defined. The interfaces for various categories of users, the response time constraints, and storage and processing needs are identified.


        Database design. A complete logical and physical design of the database system on the chosen DBMS is prepared.


        Database implementation. This comprises the process of specifying the conceptual, external, and internal database definitions, creating the (empty) database files, and implementing the software applications.


        Loading or data conversion. The database is populated either by loading the data directly or by converting existing files into the database system for-mat.


        Application conversion. Any software applications from a previous system are converted to the new system.


        Testing and validation. The new system is tested and validated. Testing and validation of application programs can be a very involved process, and the techniques that are employed are usually covered in software engineering courses. There are automated tools that assist in this process, but a discussion is outside the scope of this textbook.


        Operation. The database system and its applications are put into operation. Usually, the old and the new systems are operated in parallel for a period of time.


        Monitoring and maintenance. During the operational phase, the system is constantly monitored and maintained. Growth and expansion can occur in both data content and software applications. Major modifications and reorganizations may be needed from time to time.


Activities 2, 3, and 4 are part of the design and implementation phases of the larger information system macro life cycle. Our emphasis in Section 10.2 is on activities 2 and 3, which cover the database design and implementation phases. Most databases in organizations undergo all of the preceding life cycle activities. The conversion activities (4 and 5) are not applicable when both the database and the applications are new. When an organization moves from an established system to a new one, activities 4 and 5 tend to be very time-consuming and the effort to accomplish them is often underestimated. In general, there is often feedback among the various steps because new requirements frequently arise at every stage. Figure 10.1 shows the feedback loop affecting the conceptual and logical design phases as a result of sys-tem implementation and tuning.

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