Download 1. Introduction

Advanced Databases
Lectures
October 2013.
1. Introduction
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Data model
Informally, a data model is a type of data abstraction that is used to provide conceptual
representation. The data model uses logical concepts, such as objects, their properties, and their
interrelationships, that may be easier for most users to understand than computer storage
concepts. Hence, the data model hides storage and implementation details that are not of
interest to most database users.
(R. Elmasri, S.B. Navathe: Fundamentals od Database Systems, Addison-Wesley, 2011, 6th edition)
A data model is a collection of high-level data description constructs that hide many low-level
storage details. A DBMS allows a user to define the data to be stored in terms of a data model.
(R. Ramakrishnan, J.Gehrke: Database Management System, McGraw-Hill, 2007, 3rd ed)
Data model: a collection of conceptual tools for describing data, data relationships, data semantics,
and consistency constraints. A data model provides a way to describe the design of a database at
the physical, logical, and view levels.
(A. Silberschatz, H.F. Korth, S. Sudarshan: Database Systems Concepts, 6th Edition, McGraw-Hill, 2010.)
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Data models database models
The data model is a formal system used for database modelling
Data model can be:
Relational,
Object oriented,
Object-relational,
semi structured,
temporal, ...
etc…
Database model is a simplified represantaton of a segment of the real
world
Database model is based on a (logical) data model (formal system)
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Why are data(base) models important?
They represent the base for building software support or
information system
The base must be stable - if not - everything built over them
(program support to work with the database) will collapse
? What does the stability of the model mean?
? Does this mean that the model can not be changed?
The core of the model must be stable
Around the stable core, new elements required by the new
applications /requirements are added
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Advanced Databases 2013/2014
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What constitutes a good data model?
? What are the good data models (formal systems)?
? Are there good and bad data models?
? Are there the best data models?
There is no absolute good or bad data model
Some data models are more suitable for some applications
It is necessary to take into account the applicability of the model
in a given area and its limitaons → COURSE GOAL
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Data models - tools support
Basic objects
Operations
Integrity constraints
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Basic objects
Object types
Object complexity
User defined data types
Inheritance
Abstract data types
Support in tools for database modelling and program
development - CASE (Computer Aided Software Engineering)
tools, development environments (framework), a platform to
design and build information systems/software
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Operations
Language generaon for data management (3rd generaon, 4th
generation, 5th Generation, ..)
Procedurality
Expressiveness
Encapsulation
Reusability
Support in tools for database modelling and program
development
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Integrity constraints
Integrity refers to the consistency (correctness) of the information
contained in the database
Integrity constraints ensure that changes to data performed by users
do not violate data consistency
The ability to define rules for preserving the integrity at the database
level (not in the applications)
Usual integrity constraints:
Entity integrity, referential integrity, domain integrity, user defined
integrity
Business rules
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