Network Data ModelA database model that uses pointer-based data retrieval andsupports network data structures. (Augsten and Bo?hlen, n.d.) Hierarchical data modelA database model that uses pointer-based data retrieval andsupports only Hierarchical data structure. (Augsten and Bo?hlen, n.d.
) Relational Data ModelThe relational database model emerged in the 1970s andbecame prevalent during the 1980s. It uses the repetition of unique identifyinginformation to link related data. This method is somewhat slower and lessmachine efficient than pointer-based retrieval. However, changes in thestructure of a database can be accommodated relatively easily under therelational model. In addition, the relational model has a strong theoreticalbasis, rooted in a few relatively simple principles. · Astandard language called structured query language (SQL) has emerged forretrieval and processing of relational databases.
SQL is a query language thatmakes it relatively easy for end-users to access a database and retrieveselected data to answer ad-hoc questions. · Therelational model is by far the most prevalent model in use today. Due to continuingincreases in the capacity and processing speed of computers, the slower datarecovery of the relational model is no longer a major disadvantage for mostsystems.
(Hernandez, 2013)· At thesame time the flexibility and ease of use of the relational model have become moreand more important over time. The relational model was initially used primarilyfor low- to medium-volume databases. It opened up the ability to apply databasetechnology to support individuals and work groups. · Relationaldatabase technology can now provide suitable processing power even for manyhigh-volume databases. Hierarchical and network databases have been relegatedlargely to the role of legacy systems- technologies that are no longer viablefor use in new systems.
but are embedded in important ongoing systems that mustbe maintained. · Giventhe scope of some of the systems developed under the hierarchical and networkmodels, and the cost involved in replacing them, it is likely that databasesbased on the hierarchical and network models will continue to be used well intothe next century in recent years, the object-oriented data model has emerged.Object-oriented concepts were first incorporated in object-oriented programminglanguages. In object-oriented systems. methods or procedures that canbe performed on data are stored, along with the data, in objects.
Object-oriented systems also emphasize the idea that objects inheritcharacteristics from higher level classes of objects to which they belong.Incorporating these concepts into database systems adds to the power of thesystems. but also adds to their complexity. Although databases incorporatingthe concepts of the object-oriented model are commercially available, thus far.Object-oriented databases have been implemented primarilyin engineering rather than business-oriented systems. Because the relationalmodel is most commonly used for business systems developed today.(Silberschatz, Korth and Sudarshan, 2011) Data Representation in Database systemMetadata Metadata is an Information describing the nature andstructure of an organization`s data; data about data.
(Elmasri and Navathe, n.d.)Before we can begin to build a data model of a system, we must understand thetypes of logical relationships or structures that can exist among physicalelements and that must be represented in our data models. This type ofinformation is commonly referred to as metadata. Metadata encompasses allinformation about the structure of data, and restrictions on the values andstructures that data can have it is “data about data.” The datadictionary of a database can be thought of as containing metadata for thatdatabase. Although no universally accepted terminology exists to describemetadata structures, the most popular set of terms is used in the entity-relationshipmodel. We will use that terminology to describe the components of metadata.
Later in this chapter, we will formally discuss the entity-relationship model.EntityA person, place, thing or event of importance to theorganization. Anything that can be a noun can be an entity. (Hernandez, 2013)AttributesEach entity has a number of characteristic or propertiescalled attributes. If enties are nouns, we can think of attributes asadjectives describing characteristics of entities.Identification of entity occurrences (Primary Key)If the value of an attribute uniquely identifies anoccurrence of an entity, that attribute can serve as the primary key of anentity (Redmond, Wilson and Carter, 2012) . To serve as a primarykey an attribute must be unique.
It must be the case that no two occurrences door can have the same for the primary key attribute.Candidate KeyWhen an entity does not have a single attribute that uniquelyidentifies its occurrences, a combination of attributes may be used foridentification purposes. This type of primary key is called a candidated key. Note that it is possible to have an entity class that doesnot have a primary key. However, for several reasons we like to identify aprimary key for each entity class.
A specific occurrence of an entity class canbe directly accessed only if it has a primary key whose value can be specifiedby a user to identify the desired occurrence (Redmond, Wilson and Carter, 2012) . In addition, therelational model uses primary keys as the mechanism to link related entityclasses together. Finally, examination of the relationship of attributes to theprimary key of a table is an important part of “normalization” of adatabase. Normalization helps ensure that entity classes have been definedappropriately and that the boundaries between entity classes have been drawncorrectly. RelationshipA relationship between any two entities is defined by thepair of associations that exist between them. There are three possible types ofrelationship between two items: a one to one relationship, a one to manyrelationship, or a many to many relationship.
For example, in a supermarketdatabase the relationship between customers and orders is called one to many.