Table of contents
Introduction Page 6
Task 1 Page 7
Task 2 Page 10
Task 3 Page 14
Task 4 Page 17
Task 5 Page 19
Conclusion ...view middle of the document...
It must also check the schemas for consistency.” (Connolly, T. 2005 Pg. 37) This means the DBMS must ensure that each set of data relates to each other e.g. the information used from the conceptual schema needs to map between both the internal and external schemas.
Within this level, the internal schema shows “physical representation of the database on the computer. This level describes how the data is stored in the database.” (Connolly, T. 2005 Pg. 36) This uses a physical data model which then refers to the full details of the data storage and shows the access paths for the database. The internal schema requires specific data to be physically implemented into the system, which in this level can store and retrieve data.
In the above example, the internal schema would provide data for the server which would be used on a daily basis for the database of Marks and Spencer. The server would ensure it stores important data such as customer’s details which could include a record of previous orders, as well as contact details. The internal schema is important to an organisation as it stores relevant data, which can then ensure the company can predict future demands of their growing customer needs. This would then mean Marks and Spencer can predict the amount of new customers and level of demand so would then have to ensure they have relevant computer storage space for any new records.
The conceptual level is “the community view of the database. This level describes what data is stored in the database and the relationships among the data”. (Connolly, T. 2005 Pg. 36)
The conceptual level represents:
* All entities, their attributes and their relationships-
An example of this for M&S may include a promotional offer, such as 20% off selected items, in which the product would have a relationship with the warehouse where the product is stored, or the supplier whom it may be ordered from. Other relationships could include the expiration date of the promotional code, or restrictions placed on the promotional offer.
* Constraints on data-
For example, if M&S plan to launch a new product or service, only those relevant to the new plans would be able to access the data via the employee intranet, with passwords to restrict access.
The external level “consists of a number of different external views of the database” (Connolly, T. 2005 Pg. 36). The external schema provides each user with a different view of the entities and relationships which are only relevant to that particular user.
For example, M&S would have data stored such as a customer’s previous orders, and different views will have different representations of the same data. In the external schema, a customer’s account would provide them with the data related to them e.g. an itemised list of their previous orders. An M&S manager would be able to see the same information but on a more detailed scale. For...