Database design (conceptual, logical and physical design) unit 2 part 2

Unit -2
DATABASE DESIGN AND MODELS CHARACTERISTICS - PART 2
9/4/2019 DATABASE DEVELOPMENT LIFE CYCLE -UNIT 2 PART 1- BY RAM K PALIWAL 1

Database Design
Data modelling is the first step in the process of database design.
This step is sometimes considered to be a high-level and abstract
design phase, also referred to as conceptual design. The aim of this
phase is to describe:
◦ The data contained in the database
(e.g., entities: students, lecturers, courses, subjects)
◦ The relationships between data items
(e.g., students are supervised by lecturers; lecturers teach
courses)
◦ The constraints on data
(e.g., student number has exactly eight digits; a subject has
four or six units of credit only)

Database Design
In the second step
◦ The data items
◦ The relationships
◦ The constraints
are all expressed using the concepts provided by the high-level data model.
Because these concepts do not include the
◦ Implementation details,
◦ The result of the data modelling process is a (semi) formal representation of the database
structure.
This result is quite easy to understand so it is used as reference to make sure
that all the user’s requirements are met.

Database Design
The third step is database design. During this step, we might
have two sub-steps:
◦ Database logical design, which defines a database in a data model
of a specific DBMS,
◦ Database physical design, which defines the internal database
storage structure, file organization or indexing techniques.
These two sub-steps are database implementation and
operations/user interfaces building steps

Database Design
In the database design phases, data are represented using a
certain data model.
The data model is a collection of concepts or notations for
◦ Describing data
◦ Data relationships
◦ Data semantics
◦ Data constraints.
Most data models also include a set of basic operations for
manipulating data in the database.

Database Design
The database design is very much like that.
◦ It starts with users identifying the business rules;
◦ then the database designers and analysts create the database
design;
◦ and then the database administrator implements the design using
a DBMS.
The following subsections summarize the models in order of
decreasing level of abstraction
◦ External Model
◦ Conceptual Model
◦ Internal Model
◦ Physical Model

Database Design
External models
◦ Represent the user’s view of the database
◦ Contain multiple different external views
◦ Are closely related to the real world as perceived by each user
Conceptual models
◦ Provide flexible data-structuring capabilities
◦ Present a “community view”: the logical structure of the entire
database
◦ Contain data stored in the database

Database Design
◦ Show relationships among data including:
◦ Constraints
◦ Semantic information (e.g., business rules)
◦ Security and integrity information
◦ Consider a database as a collection of entities (objects) of various
kinds
◦ Are the basis for identification and high-level description of main
data objects; they avoid details
◦ Are database independent regardless of the database you will be
using

Database Design
Internal models
The three best-known models of this kind are the relational data
model, the network data model and the hierarchical data model.
These internal models:
◦ Consider a database as a collection of fixed-size records
◦ Are closer to the physical level or file structure
◦ Are a representation of the database as seen by the DBMS.
◦ Require the designer to match the conceptual model’s characteristics and
constraints to those of the selected implementation model
◦ Involve mapping the entities in the conceptual model to the tables in the
relational model

Database Design
Physical models
◦ Are the physical representation of the database
◦ Have the lowest level of abstractions
◦ Are how the data is stored; they deal with
◦ Run-time performance
◦ Storage utilization and compression
◦ File organization and access methods
◦ Data encryption
◦ Are the physical level – managed by the operating system (OS)
◦ Provide concepts that describe the details of how data are stored
in the computer’s memory

References
1. https://resources.saylor.org/wwwresources/archived/site/wp-
content/uploads/2014/12/CS403-1.10-Database-Design-2nd-Edition-CCBY.pdf
2. Database System Concepts 6th edition by korth and Sudarshan

Database design (conceptual, logical and physical design) unit 2 part 2

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Database design (conceptual, logical and physical design) unit 2 part 2