Showing posts from September 1, 2013

What is a Derived Attribute

What is a derived attribute? Give an example. Derived attributes are those whose values are created from other attributes.  These values are generated with the help of algorithms, calculations and other relevant procedures. The specifications established for calculating these derived attributes is a concern with respect to the processing aspects of the particular information system. These attributes may be integrated with the data model only in the condition that the attribute value calculation rules would be lost in the absence of the derived attributes. Database designers preferring to maintain the elegance of their designs prefer to avoid storing the derived attributes in their databases. They try to execute these derived attributes through appropriate algorithms so that they are called only when a specific query for them is made. In this manner the design elegance of the database is maintained. The most appropriate example of the usage of derived attributes is the calculati

Action When MultiValued Attributes Encountered

What two courses of action are available to a designer when a multivalued attribute is encountered? When a multivalued attribute is encountered, the designer has two alternatives which can be followed. The multivalued components can be split into its components and kept in the same entity. But the only condition with the usage of this approach is that only single entries are stored at each level. For example, CUSTOMER_TELEPHONE can be decomposed into CUST_HOMEPHN, CUST_MOBILE AND CUST_FAX_NUMBER. If the customer has more than one mobile number, then this structure will not be able to store more than a single value. Hence for each component, only a single value will be stored. The second approach involves the creation of a new entity which would comprise of the components of the multivalued components. This new entity can be linked to the entity in which the multivalued attributes were originally present. This method is most favorable and desirable when the total number of result

Database Design and Normalization Principles

The “right” database design can rarely be decided on the basis of normalization principles alone. Do you agree or disagree with this assertion? The Right Database and Normalization A database is a collection of information formatted into a table, chart, or file. Data tables are generally collections of information inputted into columns, rows and fields. Columns in each table can be selected through a primary sorting key and there may be unique keys to assist in data retrieval and input. You may have columns that are fixed in length or vary depending on the type of data that is being input. At the same time, records can also be fixed or varied. You can restrict column names and keep your column and table names case sensitive. You can develop a database in any form you desire as long as it is "normal." Normalization Characteristics There are many way to construct a database which includes the rational database plus the principles of normalization. One example include