CSC As I See it 006

Differentiate all basic data models and alternative data models:

1).Hierarchical Models-data is organized into a tree-like structure. The structure allows repeating information using parent/child relationships: each parent can have many children but each child only has one parent. All attributes of a specific record are listed under an entity type. In a database, an entity type is the equivalent of a table; each individual record is represented as a row and an attribute as a column. Entity types are related to each other using 1: N mapping, also known as one to many relationships. The most recognized example of hierarchical model database is an IMS designed by IBM.
2.)Network Model-is a data modelsconceived as a flexible way of representing objects and their relationships. Its original inventor was charles,Becham and it was developed into a standard specification published in 1969 by the CODASYL Consortium. Where the hiererchical model structures data as a tree of records, with each record having one parent record and many children, the network model allows each record to have multiple parent and child records, forming a lattice structure.

The chief argument in favour of the network model, in comparison to the hierarchic model, was that it allowed a more natural modeling of relationships between entities. Although the model was widely implemented and used, it failed to become dominant for two main reasons. Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in their established products such asnd DL/I. Secondly, it was eventually displaced by relational model the which offered a higher-level, more declarative interface. Until the early 1980s the performance benefits of the low-level navigational interfaces offered by hierarchical and network databases were persuasive for many large-scale applications, but as hardware became faster, the extra productivity and flexibility of the relational model led to the gradual obsolescence of the network model in corporate enterprise usage.

3.)Relational Models-is the easiest models to use and understand. Instead of creating files,records,owners,members,parents,or children, you create a table containing rows and columns.You design each table to eliminate redundancy and link them toghether using foreign keys.

4.)Entity-relationship model-is an abstract conceptual representation of structured data. Entity-relationship modeling is a relational schema database modeling method, used in software engineering to produce a type of conceptual data model (or semantic data model) of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created using this process are called entity-relationship diagrams, or ER diagrams or ERDs for short. Originally proposed in 1976 by Dr. Pin-Shan (Peter) Chen (陳品山), many variants of the process have subsequently been devised.

5.)Object-relational Model-similar to a relational database, but with an object-oriented database model: objects, classes and inheritance are directly supported in database schemas and in the query language. In addition, it supports extension of the data model with custom data-types and methods.

One aim for this type of system is to bridge the gap between conceptual data modeling techniques such as Entity-relationship diagram (ERD) and object-relational mapping (ORM), which often use classes and inheritance, and relational databases, which do not directly support them.