database management q1

larger file size

To support all the complex functions that it provides to users, a DBMS must be a large program that occupies a great deal of disk space, as well as a substantial amount of inter-nal memory. In addition, because all the data that the database manages for you is stored in one file, the database file requires a large amount of disk space and internal memory.

Advantages of Database Processing (9)

1. Getting more information from the same amount of data 2. Sharing data 3. Balancing conflicting requirements 4. Controlling Redundancy 5. Facilitating consistency 6. Improving Integrity 7. Expanding security 8. Increasing Productivity 9. Getting more information from the same amount of data Balancing conflicting requirements Controlling redundancy Improving integrity Increasing productivity Providing data independence

controlling redundancy

4. Controlling redundancy. With database processing, data that formerly was kept separate in nondatabase, file-oriented systems is integrated into a single database, so multiple copies of the same data no longer exist. With the nondatabase approach, each user group at Premiere Pro-ducts has its own copy of each customer ' s address. With the database approach, each customer ' s address would occur only once, thus eliminating redundancy. Eliminating redundancy not only saves space but also makes the process of updating data much simpler. With the database approach, changing a customer ' s address means making one change. With the nondatabase approach, in which data for each customer might be stored in three different places, the same address change means that three changes have to be made. Although eliminating redundancy is the ideal, it is not always possible. Sometimes, for rea-sons having to do with performance, you might choose to introduce a limited amount of redun-dancy into a database. However, even in these cases, you would be able to keep the redundancy under tight control, thus obtaining the same advantages. This is why it is better to say that you control redundancy rather than eliminate it.

facilitating consistancy

5. Facilitating consistency. Suppose an individual customer ' s address appears in more than one place. Customer 148, for example, might be listed at 2837 Greenway in one place and at 2856 Wisner in another place. In this case, the data for the customer is inconsistent. Because the potential for this sort of problem is a direct result of redundancy and because the database approach reduces redundancy, there is less potential for this sort of inconsistency occurring with the database approach

expanding security

7. Expanding security. Security is the prevention of unauthorized access to the database. A DBMS has many features that help ensure the enforcement of security measures. For example, a DBA can assign passwords to authorized users and then only those users who enter an acceptable pass-word can gain access to the data in the database. Further, a DBMS lets you assign users to groups, with some groups permitted to view and update data in the database and other groups permitted only to view certain data in the database. With the nondatabase approach, you have limited secu-rity features and are more vulnerable to intentional and accidental access and changes to data.

increasing productivity

8. Increasing productivity. A DBMS frees the programmers who are writing database access pro-grams from having to engage in mundane data manipulation activities, such as adding new data and deleting existing data, thus making the programmers more productive. A good DBMS has many features that allow users to gain access to data in a database without having to do any program-ming. These features increase the productivity of programmers, who may not need to write com-plex programs in order to perform certain tasks, and nonprogrammers, who may be able to get the results they seek from the data in a database without waiting for a program to be written for them.

providing data independence

9. Providing data independence. The structure of a database often needs to be changed. For example, changing user requirements might necessitate the addition of an entity, an attribute, or a relationship, or a change might be required to improve performance. A good DBMS provides data independence, which is a property that lets you change the structure of a database without requiring you to change the programs that access the database; examples of these programs are the forms you use to interact with the database and the reports that provide information from the database. Without data independence, programmers might need to expend a great deal of effort to update programs to match the new database structure. The presence of many programs in the system may make this effort so prohibitive that management might decide to avoid changing the database, even though the change might improve the database ' s performance or add valuable data. With data independence, management is more likely to make the decision to change the database.

balancing conflicting requirements

Balancing conflicting requirements. For the database approach to function adequately within an organization, a person or group should be in charge of the database, especially if the database will serve many users. This person or group is often called the database administrator or database administration (DBA), respectively. By keeping the overall needs of the organization in mind, a DBA can structure the database in such a way that it benefits the entire organization, not just a single group. Although this approach might mean that an individual user group is served less well than it would have been if it had its own isolated system, the organization as a whole is better off. Ultimately, when the organization benefits, so do the individual groups of users.

more difficult recovery

Because a database inherently is more complex than a simple file, the process of recovering it in the event of a catastrophe also is more complicated. This is particu-larly true when the database is being updated by many users at the same time. The database must first be restored to the condition it was in when it was last known to be correct; any updates made by users since that time must be redone. The greater the number of users involved in updating the database, the more complicated this task becomes.

improving integrity

Improving integrity. An integrity constraint is a rule that data must follow in the database. For example, the rep number given for any customer must be one that is already in the database. In other words, users cannot enter an incorrect or nonexistent rep number for a customer. A data-base has integrity when the data in it satisfies all established integrity constraints. A good DBMS should provide an opportunity for users to incorporate these integrity constraints when they design the database. The DBMS then should ensure that the constraints are not violated. According to the integrity constraint about customers, the DBMS should not allow you to store data about a given customer when the rep number you enter is not the number of a rep that already is in the database.

greater impact of failure

In a nondatabase, file-oriented system, each user has a completely separate system; the failure of any single user ' s system does not necessarily affect any other user. On the other hand, if several users are sharing the same database, a failure on the part of any one user that damages the database in some way might affect all the other users

increased complexity

The complexity and breadth of the functions provided by a DBMS make it a complex product. Users of the DBMS must learn a great deal to understand the features of the system in order to take full advantage of it. In the design and implementation of a new sys-tem that uses a DBMS, many choices have to be made; it is possible to make incorrect choices, especially with an insufficient understanding of the system. Unfortunately, a few incorrect choices can spell disaster for the whole project. A sound database design is critical to the suc-cessful use of a DBMS.

Sharing Data

The data of various users can be combined and shared among authorized users, allowing all users access to a greater pool of data. Several users can have access to the same piece of data — for example, a customer ' s address — and still use it in a variety of ways. When one user changes a customer ' s address, the new address immediately becomes available to all users In addition, the existing data can be used in new ways, such as generating new types of reports, without having to create additional data files, as is the case in the nondatabase approach

Getting more information from the same amount of data

The primary goal of a computer system is to turn data (recorded facts) into information (the knowledge gained by processing those facts). In a non database, file-oriented environment, data often is partitioned into several disjointed systems, with each system having its own collection of files. Any request for information that necessitates accessing data from more than one of these collections can be extremely difficult to fulfill. In some cases, for all practical purposes, it is impossible. Thus, the desired information is unavailable — it has been stored in the computer, but it is scattered across multiple files. When all the data for the various systems is stored in a single database, however, the information becomes available. Given the power of a DBMS, the information is available, and the process of getting it is quick and easy.

Disadvantages of database processing (4)

larger file size increased complexity greater impact of failure more difficult recovery