Tuesday, June 15, 2010

ECP3076 tut 1

1. Describe the different ways a DBMS can be classified.
• No of users, locations, expected type and extend of use

2. A relational database differs from network and/or hierarchical databases in what aspect(s)?
- Physical structure closely resembles the logical structure.
- The relational DBMS handles most physical details.

3. Describe the basic features of the relational data model and discuss their importance to the end user as well as the designer.
- The relational data model illustrates end user data as beong stored in tables. Each table is a matrix consisting of a series of row/column intersections. Tables also called relations are related to each other by sharing of a common entity characteristic (value in a column). The relational database is perceived by the user to be a collection of tables in which data are stored. The relational data model allows the designer to focus on how the data components interact rather than on the physical details of how the data are store. The makes much easier to model the complex real world data environment.

4. Explain structural independence and its importance in data management.
- In terms of data management, structural independence means that the way the data is stored will have no effect on the programs that use it. In other words, any changes to the file structure will not effect existing programs that access the data stored within the file structure. File system data management is an example of data structure that does NOT show structural independence – program access is tied tightly with how data is stored. DBMS structures support better structural independence as the user no longer need to know where/what is used to store the data but only how to access it.

a) What problems can you identify with the data file structure shown above? How can they be corrected?
- Table shows data from 2 separate ‘objects’ – projects and managers, results in redundant copies of data which increase occurrence of data anomalies – insertion, deletion and update anomalies. At current structure, multiple copies of same data MUST be created even though real life the relationship does not exist such as:
- 1. A new manager in the company can only be inserted once he/she is assigned a project.
- 2. Projects must have a manager at time of data insertion into the table.
- 3. Other employee data is not listed as project members except the manager.
- 4. If Holly gets married, her last name has to be changed three times (update)
- 5. Information about “William K. Moor” will be lost if his row is deleted. (delete)
- To correct the problems the file structure can be subdivided into simpler files, each representing a single subject – i.e. Normalization.