Overview of the Flat-File versus Database Approach

Overview of the Flat-File versus Database Approach

Many so-called legacy systems are characterized by the flat-file approach to data management. In this environment, users own their data files. Exclusive ownership of data is a natural consequence of two problems associated with the legacy-system era. The first problem is a business culture that erects barriers between organizational units that inhibit entity-wide integration of data. The second problem stems from limitations in flat-file management technology that require data files to be structured to the unique needs of the primary user. Thus, the same data, used in slightly different ways by different users, may need to be restructured and reproduced in physically different files. Figure 9-1 illustrates this model.

In the figure, the file contents are represented conceptually with letters. Each letter could signify a sin- gle data attribute (field), a record, or an entire file. Note also that data element B is present in all user files. This is called data redundancy and is the cause of three types of data management problems: data storage, data updating, and currency of information. Each of these, as well as a fourth problem—task- data dependency, which is not directly related to data redundancy—will be examined next.

DATA STORAGE

Chapter 1 showed that an efficient information system captures and stores data only once and makes this single source available to all users who need it. This is not possible in the flat-file environment. To meet the private data needs of users, organizations must incur the costs of both multiple collection and multiple storage procedures. Indeed, some commonly used data may be duplicated dozens, hundreds, or even thousands of times, creating excessive storage costs.

DATA UPDATING

Organizations have a great deal of data stored on master files and reference files that require periodic updating to reflect operational and economic changes. For example, a change in a customer’s name or

address must be reflected in the appropriate master files. This piece of information may be important to several user departments in the organization, such as sales, billing, credit, customer services, sales promotion, and catalog sales. When users maintain separate files, any such change must be made separately for each user. This adds significantly to the cost of data management.

CURRENCY OF INFORMATION

In contrast to the problem of performing multiple updates is the problem of failing to update the files of all users affected by a change. If update messages are not properly disseminated, then some users may not record the change and will perform their duties and make decisions based on outdated data.

TASK-DATA DEPENDENCY

Another problem with the flat-file approach is the user’s inability to obtain additional information as his or her needs change. This problem is called task-data dependency. The user’s information set is con- strained by the data that he or she possesses and controls. For example, in Figure 9-1, if the information needs of User 1 change to include Data L, User 1’s program would not have access to these data. Although Data L exists in the files of another user, keep in mind the culture of this environment. Users do not interact as members of a user community. They act independently. As such, User 1 may be unaware of the presence of Data L elsewhere in the organization. In this environment, it is difficult to es- tablish a mechanism for the formal sharing of data. Therefore, Data L would need to be recreated from scratch. This will take time, inhibit User 1’s performance, add to data redundancy, and drive data man- agement costs even higher.

THE DATABASE APPROACH

Figure 9-2(a) presents a simple overview of the database approach with the same users and data requirements as in Figure 9-1. The most obvious change from the flat-file model is the pooling of data into a common database that is shared by all the users.

FLAT-FILE PROBLEMS SOLVED

Data sharing (the absence of ownership) is the central concept of the database approach. Let’s see how this resolves the problems identified.

• No data redundancy. Each data element is stored only once, thereby eliminating data redundancy and reducing storage costs.

• Single update. Because each data element exists in only one place, it requires only a single update pro- cedure. This reduces the time and cost of keeping the database current.

• Current values. A change any user makes to the database yields current data values for all other users. For example, when User 1 records a customer address change, User 3 has immediate access to this cur- rent information.

• Task-data independence. Users have access to the full domain of data available to the firm. As users’ information needs expand beyond their immediate domain, the new needs can be more easily satisfied than under the flat-file approach. Only the limitations of the data available to the firm (the entire data- base) and the legitimacy of their need to access it constrains users.

CONTROLLING ACCESS TO THE DATABASE

The database approach places all the firm’s information eggs in one basket. It is essential, therefore, to take very good care of the basket. The example in Figure 9-2(a) has no provision for controlling access to the database. Assume Data X is sensitive, confidential, or secret information that only User 3 is authorized to access. How can the organization prevent others from gaining unauthorized access to it?

THE DATABASE MANAGEMENT SYSTEM

Figure 9-2(b) adds a new element to Figure 9-2(a). Standing between the users’ programs and the physical database is the database management system (DBMS). The purpose of the DBMS is to provide con- trolled access to the database. The DBMS is a special software system that is programmed to know which data elements each user is authorized to access. The user’s program sends requests for data to the DBMS,

which validates and authorizes access to the database in accordance with the user’s level of authority. The DBMS will deny requests for data that the user is unauthorized to access. As one might imagine, the organization’s criteria, rules, and procedures for assigning user authority are important control issues for accountants to consider.

THREE CONCEPTUAL MODELS

Over the years, several different architectures have represented the database approach. Early database models are as different from modern database models as they were from traditional flat files. The most common database approaches used for business information systems are the hierarchical, the network, and the relational models. Because of certain conceptual similarities, the hierarchical and network databases are termed navigational or structured models. The way that data are organized in these early database sys- tems forces users to navigate between data elements using predefined structured paths. The relational model is far more flexible by allowing users to create new and unique paths through the database to solve a wider range of business problems.

Although their limitations are severe and their ultimate demise is inevitable, hierarchical and network models still exist as legacy systems that support mission-critical functions in some companies. Most modern systems, however, employ relational databases. The main text of the chapter focuses on the relational model. The key features of structured database models are outlined in the chapter appendix.