Summary

1. The file hierarchy begins with bytes (the smallest addressable units), which make up data items. Data items are records that are grouped to make up a file: Two or more files are a data base:

2. There are four methods of organizing files:

   a. Sequential organization means storing records in contiguous blocks according to a key.

   b. Indexed-sequential organization stores records sequentially but uses an index to locate records. Records are related through chaining using pointers.

   c. Inverted list organization uses an index for each key type. Records are not necessarily in a particular sequence.

   d. Direct-access organization has records placed randomly through­ out the file. Records are updated directly and independently at other records.

3. A data base is a collection of interrelated data stored with a minimum of redundancy to serve many applications. Data base design minimizes the artificiality embedded in using separate files. The primary objectives are fast response time to inquiries, more information at low cost, control of redundancy. Clarity and ease of use, data and program independence, accuracy and integrity of the system, fast recovery, privacy and security of information, and availability of powerful end user languages.

4. The heart of a data base is the DBMS. It manages and controls the data base file and handles requests from the application program in a data manipulation language (DML). To produce the user's view, the data model represents data structures and describes the view in a data definition language (DDL). DDL simply tells the DBMS how the data must be structured to meet application program requirements. DML, then, manipulates -data; DDL describes and identifies data structures; and the DBMS manages and coordinates data according to DML re­ quests and DDL descriptions.

5. A data structure defines relationships among entities. There are three types of relationships: one-to-one, one-to-many, and many-to-many relationships. Data structuring in a DBMS determines whether the system can create a given relationship between entities.

6. Although all DBMSs have a common approach to data management, they differ' in the way they structure data. The three types of data structures are hierarchical, network, and relational. A hierarchical structure specifies that an entity cannot have more than one parent. A network structure allows 1:1, l:M, or M:M relationships and can best be supported by a network. To simplify the structure; the network is separated into a number of hierarchies with duplicates. A hierarchy, then, becomes a sub view of the network structure. A relational structure is a flat, two-dimensional table representing data and relationships. It allows the user to update the table's content and provides a powerful inquiry capability.

7. There are four views of data. The first three views are logical: user's view, application program (called subschema), and overall logical view (called schema). The physical view is what the data actually look like in physical storage.

8. The data structure can be refined through a normalization process that groups data in the simplest way possible so that later changes can be made with ease. Normalization is designed to simplify relationships and establish logical links 11etween files without losing information. An inherent problem is data redundancy and the inefficiency it generates.

9. Managing the data base requires a data base administrator (DBA) whose key functions are to manage data activities, the data base structure, and the DBMS. In addition to a managerial background, the DBA needs technical knowledge to deal \with data base designers. Important for the success of this important job is the support of the senior MIS staff and upper management for the overall data base function.