Every relationship type has a specific symbol to

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Every relationship type has a specific symbol to implement it.
Database Modeling and Normalization5Among the various types of cardinality notation, crow's foot notation is the most commonly used. With this type of notation, a single bar indicates one, a double bar indicates one and only one, a circle indicates zero, and a crow's foot indicates many.Define Primary Keys A primary key is used to uniquely identify each row in a table. It can either be part of the actual record itself, or it can be an artificial field (one that has no meaning other than being an identifier of the record). A primary key cannot be NULL, as it does not make sense to use the NULL value to uniquely identify a record. Therefore, the column that is set as a primary key or as part of a primary key cannot be NULL. Primary keys can be specified either when the table is created or by changing the existing table structure.How primary keys are set up is an important factor in database design, as the choices of primary key can have significant impact on the performance, usability, and the extensibility of the entire database. In designing the primary key, it is best to use as few columns as possible. This is for both storage and performance reasons. Since primary key information requires additional storage in a relational database, the more columns a primary key includes, the more storage it requires. In terms of performance, fewer columns mean that the database can process through the primary key faster since there is less data, and it also means that table joins will be faster since primary keys, together with foreign keys, are often used as the joining condition.Draw Fully-Attributed ERD After identifying new entities and attributes in step 8, the ERM diagram needs to be
Database Modeling and Normalization6redrawn. Rearranging lines so that no lines cross by putting the entities with the most relationships in the middle. When designing an ERM diagram, an entity is represented as a rectangle containing the name of the entity. The names of attributes are enclosed in an oval connected to the rectangle of the entity they describe. Attributes may be omitted from the diagram to avoid cluttering it and also in the early stages of development. Relationships are represented by diamonds between entities. The notation of the ERD, however, varies according to the modeling approach used.Lastly it is important to verify the diagram from the point of view of a system user. Checking cardinality pairs and looking over the list of attributes associated with each entity is necessary to see if anything has been omitted. “This step cleans up some of the shortcomings of the ERD created so far. In particular, it involves eliminating many-to-many relationships, and adding primary and foreign keys for each entity” (CQU, 2006).

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