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Why analyse data?

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Data Analysis Why analyse data? A basic form of database is a flat file of data. The file is made up of a series of records and each record has a series of fields in it. Top of File First Record Last Record Bottom of file Records may be fixed length (padded with spaces) or variable length (e.g. comma delimited). As we move to more complex applications, the type of data we work with expands. Eventually the flat file or single table becomes unsuitable. There may be many users that need to get access to the data for view or edit. Having more that one user updating the file at once causes problems. Different areas of the program may require access to different parts of the data. If the data is organised, smaller amounts need to be open for update. This improves accessibility and therefore performance. Speed of access reduces with increasing record count and record length. Often there are a number of similar items on a record e.g. exam results against a pupil on a student record (how many subjects, how many papers, how many slots do you need?). Organising you data in to different files or tables allows greater flexibility. Organising your data can be a difficult process, particularly with large systems with hundreds of tables. There are methods of analysis, which help us to avoid these problems. ...read more.


Attributes are the data types that are specific to the entity. In the library example, the entity CUSTOMER has ATTRIBUTES of ID, Name, address, contact number, limit and status. Attributes have DOMAINS. The domain of the attribute (field) is the set of values that are contained in the attribute across all the records. Looking at the entity 'Customer' in the library example, the attribute 'Name' would have a domain containing the names of all the customers and Status would have a domain of containing the different states of a customer account e.g. blocked, closed, normal The Entities also have RELATIONSHIPS with each other. The relationship between the keys of two entities operates in both directions. The relationship between Customer and loans would be described as 'A Customer may have one or more Loans' and 'A Loan must belong to one customer'. The relationship contains information telling us if a record in one table can exist with out a partner record in another table. Here, a loan can not exist with out a customer but clearly a customer may exist who never uses the library and never has a loan. In relational databases such as Oracle, Ingress and Access, these relationships can be enforced so that you can not enter a loan record for a customer that does not appear in the customer database. Below is one representation of this relationship. It can also be represented using 'crows feet' for Many and a single straight line as One. ...read more.


Entity Attribute Loan Loan ID ISBN Code Borrower ID Borrower name Date out Date due back Fine Due Times Renewed If Borrower name did not already exist in Customer, we would need to create a new entity for it. Since it does already exit, its appearance in this entity was purely data redundancy so it can be removed entirely. Entity Attribute Loan Loan ID ISBN Code Borrower ID Date out Date due back Fine Due Times Renewed This is now in 3rd Normal Form. We can see that by normalising the data we have generated extra entities, which will in turn have relationships. The process is iterative and for major systems, teams of analysts have 'walk through' sessions to ensure accuracy of the data structure. Normalisation becomes almost second nature after a while. The problems are often dealt with in the E-R Modelling stage with out realising it because much of it is common sense. It is still a useful tool to double check that you have not missed anything. Final Structure Entity Attribute Customer Borrower ID Name Address Contact Number Account Status Customer Media Details Media Type Borrower ID Media Limit Media Status Media Media Type Media Description Loan Loan ID ISBN Code Borrower ID Borrower name Date out Date due back Fine Due Times Renewed Book ISBN Code Title Author Publisher Loan Period NB This data model does not cater for multiple copies of a book. Also, the other media types may not have ISBN numbers. Systems Analysis 13/11/00 Page 1 of 8 ...read more.

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