Databases are used to store data, facilitate access to records and allow relationships between different types of records. There is a wide variation in levels of sophistication and complexity, ranging from card index system to system containing all the basic data required to run a business.
Types of Database Structures Having Different Levels of Sophistication:
a. Hierarchical databases
b. Network database
c. Relational database
a. Hierarchical Databases:
Hierarchical Databases is most basic type of database, having a simple hierarchical structure. Each data Item is related to only one item above it, although it may be related to any number of items below.
Hierarchical also celled tree databases specifies that an entity can have no more than one owning entity; that is we can establish 1:1 or 1:M relationship . The owning entity is called the parent; the owned entity is called the child. A parent with no owner is called the root. There is only one root in a hierarchical model.
The hierarchical model is easy to design and understand, but is less appropriate when there is a more complex relationship between data items. For example see the diagram below:
This structure is unsatisfactory on two counts:
- There may be more than one supplier for each stock item, which would necessitate having a number of different fields to allow for the different suppliers.
- One supplier is likely to supply different stock items. This would mean that the same data would have to be held on file several times (data redundancy) and would also make enquiries based on the supplier to be more difficult. A list of all products bought from one supplier would require all of the records to be read, an expensive and time consuming process.
(b). Network Database:
A network database allows 1:1, 1:M or M:M relationships among entities. For example, computer accessories selling shop may have dealing with more than one computer manufacturers (parent). In figure below computer accessories comes from Compaq and Dell. Now consider the computer manufacturer and the seller shops it deals with. If the manufacturer sold computers to only one shop (Perfect Soft), then there is a 1:1 relationship. If it supplied many other dealers, then there is a 1:M relationship. The 1:1 and 1:M relationships can be supported by a hierarchical database. When computer accessories are supplied by many computer manufacturers, however, there is a M:M relationship, which is a network structure.
The solution to draw a network database is to separate the network into several hierarchies with duplicates. This simplifies the relationship to no more complex than 1:M. A hierarchy, then, becomes a sub-view of the network structure.
(c). Relational Databases:
A relational databases is more complex structure which allows both 1:M and M:M relationships with the minimum duplication of data. Data is split between different tables which are linked together via asset of unique keys.
|Difference between MIS & DSS
- Generate regular reports as a tool for decision making.
- Not necessarily interactive.
- Decision making not necessarily immediate.
- Predefined format.
- Support lower & middle level management.
- MIS can be either manual or computerized.
- No prior knowledge of
computer is required.
- There are no regular reports.
- Always interactive.
- Decision making generally immediate.
- Tailored made situation.
- Support middle and higher level management.
- DSS should always be computerized for the facilities of using the databases.
- Medium level computer literacy is required for manipulate the database.