AIS - CHAPTER 5

DATA BASE SYSTEMS

Data Bases

• Data base approach focuses on data integration and data sharing, views data as an organizational resource



• Data Base Management System (DBMS) refers to programs that control the data and interfaces between the data and application programs



• The data based, DBMS, and the application programs together are termed as data base system

• Data base administrator is the person responsible for the data base.



• Data base systems separate logical and physical views of data, referred to as program-data independence
• Logical view - how the user or programmer conceptually organizes and understands data
• Physical view - how and where the data are physically arranged and stored on storage medium



• Advantages of program-data independence
• Application programmers can code application logic without concern for physical storage
• the logical view of the task can be changed without changing the physical data storage



• Schema - logical structure of the data base

1. Conceptual level schema - organization wide view of entire data base
2. External level schema - individual user views of data, subschema
3. Internal level schema - low-level view of data based, how data are stored
4. DBMS translates user requests at logical level into physical actions
5. Accountants are involved with conceptual and external levels, rarely the internal level.

• Data Dictionary - information on the structure of the data base

1. Each data element is described in detail.
2. Usually maintained automatically by DBMS
3. Output of data dictionary often includes
1. Programs where data items are used.
2. List of synonyms
3. Data elements used by a user
4. List of output reports where data element is used.

• DBMS languages - functions of creating, changing and querying

1. Data definition language (DDL) - build data dictionary, initialize, describe logical views, specify security imposed on users.
2. Data manipulation language (DML) - data maintenance, updating, inserting and deleting, references only data names.
3. Data query language (DQL) - interrogation of the data base - retrieves, sorts, orders and presents subsets of data
4. Report writer - simplifies report creation, user specifies data elements and format.

Relational DBMS

• Relational data model represents everything in the data base as being stored in the form of two-dimensional tables (relations)

1. Rows are called tuples - analogous to records in a file.
2. Columns represent specific characteristics (attributes) - like fields.

• Constraints imposed by relational model

1. Primary keys must be unique - entity integrity rule - specifically identifies a row in a table.
2. Every foreign key must be either null or have a value corresponding to the value of a primary key in another relation - referential integrity rule - foreign keys link tables together.
3. Each column in a table must describe a characteristic of the object identified by the primary key.
4. Each column in a row must be single-valued.
5. he values in every row of a specific column must be of the same data type
6. Neither column order nor row order is significant.

• Potential problems with relational models

1. Update anomaly - inconsistencies that may occur by not changing every occurrence of a data item - (solve: store data items only once).
2. Insert anomaly - inability to insert new data without violating basic integrity rules - (solve: maintain different tables for entities)
3. Delete anomaly - removal of desired information because of the deletion of a transaction - (solve: separate tables for entities.)

• Normalization - the process of structuring a data base for efficiency and to eliminate anomalies.

Data Base Design

• The design and operation of a data base system consists of six stages -- Planning, Design, Coding, Implementation, and Operation and Maintenance

• Planning - determine the need for and technological and economic feasibility of developing a new data base system



• Requirements analysis - identifying user needs, defining scope, hardware/software requirements



• Design - development of the actual structure of the data base
• Conceptual design/conceptual schema - translate the data requirements for various users into a conceptual model, can be implemented in any DBMS
• Logical design - implementation of the conceptual model in a specific type of DBMS
• Physical design - development of actual data base structures (tables), develop new applications, modify existing applications



• Coding - translate physical schema into actual data base structures (tables), develop new applications, modify existing applications



• Implementation - testing the system, transferring data from existing files to a new data base, and training the users



• Operation and Maintenance - monitoring the system performance and user satisfaction, enhancing and modifying the system, watching for obsolescence



• Role of the accountant - can be involved in every stage; however, the depth of involvement may vary depending on the expertise of the accountant

Data Base Systems and the Future of Accounting

• Could lead to the abandonment of double-entry accounting - redundancy is not longer needed.



• External reporting may become a matter of data base access by users.



• DBMS provides users with powerful ways to access data without filtering by accountants.



• The use and value of accounting information can become greater for strategic and tactical decision making.



• Accountants must be active participants in designing systems to see that adequate controls are included to safeguard the data and reliability of the information.

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