Database design – data modelling and database models
data modelling is conceend with the design of the database. it is a technique for organising and documenting a system’s data. it is sometimes called database modelling because a data model is eventually implemented as a database.
database design is based on a particular model and there are sevral conceptual models used .
The real world is the application for which the database is intended for .it is modeled based on events and , operation and data using a database model.
The system is then developed using a DBMS and implemented for a particular information retrieval system for the end user.
data modelling is perhaps the most labor-intensive and time-consuming part of the database development but is critical to the development because development without a model is as problematic as building a house without blueprints.
it is unprofessional to build a database without a model because the usability and performance of such a database is at a serious risks.
The following needs for data model are identified.
* To ensure that all the data objects required by the database are completely and accurately represented.
* the data model provides enough detail to be used by the database developers as a blueprint for building the physical database.
* The information in the data model will be used to define the relational tables, primary and foreign keys, stored procedures, etc. in the case of relational database.
* A poorly designed database will require more time in the long run. Without careful planning you may create a database that omits data required to create critical reports, procedures result that are incorrect or inconsistent, and unable to accommodate changes in the user’s requirements.
Data modelling is needed to efficiently and accurately specific data required by a database so as to efficiently store and access data in the database.
database design surrounds around the design of thehe logical and physiacal structure of one or more database to accommodate the information needs of the usrs in an organisation for a different applications.
The design process may follow the other underlisted five steps.
(i) planning and analysis (ii) Conceptual design (iii) Logical design (iv) physical design (v) implementation.
The data model is one part of the conceptual designs process. The other, typically is functional model.
The data model focuses on what should be stored in the database while the functional model deals with how the data is processed.
Data model is used to design the tables, while the functional model is used to design the queries which will assess and perform operations on those tables.
the data model takes ans input from the planning stage. Here the modeler, along with analyst, collects information about the requirement of the database by reviewing existing documents and interviewing end-users.
The data model has two outputs. The first is an entity – relationship diagrams which represents the data structure in a pictorial form. The diagram is easily learned , therefore ,it is a valuable tool to communicate the model to the end user.
Second component is a data document. This is a document that describes in detail the data ,objects relationships, and rules required by the database.
The dictionary provides the details required by the database developer to construct the physical database.
Various techniques are used to model data structure . Certain models are more easily implemented by some types of database management systems than others.
For any one logical model various physical implementations may be possible .
An example of this is the relational model : in larger systems the physical aspects of common implementations of the network model.
But in small relational database the data is often stored in a set of files ,one per table ,in a fiat , indexed structure.
A data model is derived from perceived reality .
Database Model Definition
A database model is a theory or specification describing how a database is structured and used.
It is a collection of conceptual tools for describing data , data relationship , data semantics , and consistency constraints.
The university of texas at Austin , defines data model as a conceptual representation of data structures that are required in a database.
The data structures include the data objects , he associations between data objects , and the rules which govern operations on the objects.
Basically a data model does not only represent the data objects but also the relationship between the data objects and the rules guiding the operation on the data objects.
Data model is principally aimed at ensuring that all data required by the database are completely and accurately represented.
The model is used by database developer as ” blue print ” for building physical database. Building a database without a model is like building a house without a design. Modelling is the most intensive aspect of developing a database.
Database models examples
Common database models types includes
* Entity – relationship model
* Relational model
* Hierarchical model
* Network model
* Object – oriented model
– The entity relationship model uses four basic concepts to represent the real world . It is simple but lack any existing machine to implement it directly.
– Network model allows multiple dataset to be used together through the use of pointers ( or references ) . Some columns contain pointers to different tables instead of data . Thus , the table are related by references , which can be viewed as a network structure.
– Hierarchical model limits the Relationship to a tree structure, instead of the more general directed graph structure implied by the full network model.
– Relational model contains multiple tables , each similar to the one in the ” flat ” database model .
However unlike network database, the tables are not linked by pointers . Instead , ” keys ” are used to match up rows of data in different tables .
A key is just one or more columns in a table , which correspond to columns in other tables . Any of the columns in a table can be a key or multiple columns can be grouped together into a single key online point is it’s not necessary to define all the keys in advance a column can be used as a key even if it wasn’t originally intended to be one
Database design – data modelling and database models are all Important concept every developer must be aware of.