A hierarchically structured database is arranged logically in an inverted tree pattern Hierarchical Database Model All records in hierarchy are called Nodes. Each node is related to the others in a parent- child relationship. Each parent record may have one or more child records, but no child record may have more than one parent record. The top parent record in the hierarchy is called the Root Record. 18. Explain the Network Database Model in detail. a) The network model is able to represent redundancy in data more efficiently than in the hierarchical model. b) In network model a relationship is a set. Each set is made of at least two types of records. An owner record (Parent in Hierarchical) and a member record (child in Hierarchical). The difference is network model allows a record to appear as a member in more than a set. c) This feature allows the network model to implement the one-to-one, one-to many, many-to-one and the many-to-many relationship types. Features: • It is a modified version of Hierarchical Data model. Children of Equipment Children of Room Parents of Repair Children of Building Parents of Equipment Root Parent of Room Building 1 Room 1 Equip 1 Repair 1 Repair 2 Equip 2 Room 2 Equip 3 Repair 3
Enterprise Information System 8 • It is very difficult to develop this type of database structures. • It is useful for one to one, one to many, many to many and many to many record relationships. • The relationships should be pre-determined 19 . Explain the Relational Database Model in detail. A Relational Database allows the definition of data and their structures, storage and retrieval operations and integrity constraints that can be organized in a table structure. A table is a collection of records and each record in a table contains the same fields, which define the nature of the data stored in the table. A record is one instance of a set of fields in a table. Three key terms are used extensively in relational database models: Relations, Attributes, and Domains. A relation is a table with columns and rows. The named columns of the relation are called attributes, and the domain is the set of values the attributes can take. All relations (and, thus, tables) in a relational database must adhere to some basic rules to qualify as relations. First, the ordering of columns is immaterial in a table. Second, there can’t be identical record in a table. And third, each record will contain a single value for each of its attributes. A relational database contains multiple tables, with at least similar value occurring in two different records (belonging to the same table or to different tables) that implies a relationship among those two records. In a relational database, all the tables are related by one or more fields, so that it is possible to connect all the tables in the database through the field(s) they have in common. For each table, one of the fields is identified as a Primary Key, which is the unique identifier for each record in the table. Keys are commonly used to join or combine data from two or
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- Spring '20
- Operating Systems, Database management system, Computer data storage