A proper physical database design is one of the most important steps that a database designer can complete to impact the overall performance of the database. When doing the physical database design it is important for the designer to understand what type of data is going to be included and how this data will be used. To better understand why this is important lets first break down a few of the basic elements that are important when completing the physical database design.
One of the most basic measures that most be examined and planned involves the smallest units within the database, the fields. The fields are derived from the simple attributes that were defined in the logical data model. A few decisions need to be made regarding each of these individual fields. First what type of data is going to be storied in them? The data type that is assigned to each field should be able to accurately represent every possible valid value, while limiting invalid values as much as possible. Special consideration should be taken for any manipulations that will be done on the data as some data types allow these manipulations a lot easier than other ones. When considering data manipulations it is important to keep in mind simple things like addition, if finding the sum of the data field’s values the data type that worked for the fields may not be large enough to support the resulting summation.
Related to the actual data type chosen, are a number of other controls that can be attached to the fields to better insure the integrity of the data. One of these controls is simple the default value that the field should take, unless another value is assigned to it. If done correct, defining a default value can be very beneficial as it coul...
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...grity can be implemented and the performance impact can be minimized. When looking at some of the more advanced design methods mentioned it is critical to understand the data and how it is used, it also doesn’t hurt to have a few tools to help you along the way.
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The relational model consist of a relational structure, a set of integrity rules, and data manipulation operations. The relational structure is based on the representation of data in the form of tables. A table contains rows and columns, with each row representing an individual record, and each column representing a field for each record. Tables are related via indirect indexes of primary and foreign keys. The operations that are performed on these tables in order to store, manipulate and access this data include union, intersection, join, division, restriction, projection, assignment, difference, and product.
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...el that's closely aligned with the software program’s object model. Obviously, an OODBMS may have a physical data model optimized for those types of logical data model it needs.
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[7] Elmasri & Navathe. Fundamentals of database systems, 4th edition. Addison-Wesley, Redwood City, CA. 2004.
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