Database approaches is a methodology used by the database designer to develop the database for the proposed system. In present developers use two types of approaches to design the database through different types of database language. Such approaches are follows,
- Top down approach
- Bottom up approach
Top down approach
Top down approach is a one of the database approach which will follows as the main parts to smaller parts. This approach is based on the entity relationship (ER) diagram. First the developer will identify the major parts of the proposed system and later the developer will find out the smaller parts of the database by getting the requirements from the system users. In this approach, the main part is considered as the tables and small parts will be considered as field. The table can be called as entity and fields can be called as attributes in entity relationship diagram. The developer can identify the entities from the proposed system plan and he/she should discuss with the system user to find the necessary attributes as the attributes are the data which will be stored by the users. This approach can be used for the small proposed system as it is easy to find the entities from the small proposed system.
Advantages of top down database model
- ER diagram will be drawn and used for the development of database system.
- Easy to add more attributes when needed by modifying the tables as the relationship between the table is not much complex.
- The developer can easily find the necessary tables at the beginning so the time taken for the database development will be low when compare with bottom up approach.
Limitations of top down database model
- The developer must go through the full scenario or the full requirements to find the table names and need to find the relationship at the beginning.
Bottom up approach
This is another type of approach used by the database developers in present days. This approach can be considered as the opposite of top down approach because in this methodology first the developer will find out the required data which should be stored by the users through the system to manage them in future by discussing with the end users and find out the necessary attributes. Then the developer will follow the normalization method and will do the normalization until the 3rd level normalization. By doing the normalization developer can filter the attributes to tables which means entity and finally find out the required entity for the database. This methodology can be used for the complex and the large systems and mainly for the system which is difficult to find out the necessary tables directly.
Advantages of bottom up database model
- Normalization method will be used to develop the database.
- Duplication of data can be stopped by doing different levels of normalization.
- No need to find the relationship at the beginning.
- The developer can know the required attribute at the beginning so the developer can identify the data which are needed to store on the database.
Limitations of bottom up database model
- Difficult to add attributes to the entity as the entity will be designed based on the previously collected attributes.
- Complex relationship will be formed.
- Difficult to find all the required attribute at the beginning.