Advanced Databases Lectures October 2013.

Transcription

1 Advanced Databases Lectures October Introduction ZPR-FER - Zagreb Advanced Databases 2013/2014 1

2 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, 6 th 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, 6 th Edition, McGraw-Hill, 2010.) ZPR-FER - Zagreb Advanced Databases 2013/2014 2

3 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) ZPR-FER - Zagreb Advanced Databases 2013/2014 3

4 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 ZPR-FER - Zagreb Advanced Databases 2013/2014 4

5 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 limita ons COURSE GOAL ZPR-FER - Zagreb Advanced Databases 2013/2014 5

6 Data models - tools support Basic objects Operations Integrity constraints ZPR-FER - Zagreb Advanced Databases 2013/2014 6

7 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 ZPR-FER - Zagreb Advanced Databases 2013/2014 7

8 Operations Language genera on for data management (3rd genera on, 4th generation, 5th Generation,..) Procedurality Expressiveness Encapsulation Reusability Support in tools for database modelling and program development ZPR-FER - Zagreb Advanced Databases 2013/2014 8

9 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 ZPR-FER - Zagreb Advanced Databases 2013/2014 9