CSC2012 Database Technology & CSC2513 Database Systems

2 Recommended texts Essential: Recommended:  Raghu Ramakrishnan and Johannes Gehrke. Database Management Systems Some of my slides based on this book; covers DBMS internals (how to build a DBMS)  T Connolly & C Begg, Database Systems. A Practical Approach to Design, Implementation and Management, (either 3 rd or 4 th ed OK) Used for CSC2002 before Background:  R Elmasri & S B Navathe. Fundamentals of Database Systems

3 What is a Database? A collection of data (and a description of this data), which is  logically related  Typically, designed to meet the information needs of an organization. Databases play a critical role in almost all areas where computers are used, including business, engineering, medicine, law, education, library, to name a few. A database can be of any size and of varying complexity.  the list of names and address of friends  The book catalog of a large library may contain a million records  A database of much greater size and complexity is maintained by the government to keep track of the tax information filed by taxpayers.

4 Database Management System DBMS (Database Management System): a software system that enables users to define, create, and maintain the database and that provides controlled access to this database. Provides a Data Definition Language (DDL)  Allows specification of data types, structures and any data constraints. Also provides a Data Manipulation Language (DML)  General enquiry facility (query language) of the data.  Most common query language: SQL (Structured Query Language)

5 DBMS -- Why Bother? Alternative: File-based systems  Collection of application programs that perform services for the end users.  Each program defines and manages its own data.  Most languages support file operations

6 File-Based Systems – Limitations Separation and isolation of data  Each program maintains its own set of data.  Users of one program may be unaware of potentially useful data held by other programs. Duplication of data  Same data is held by different programs.  Wasted space and potentially different values and/or different formats for the same item.

7 File-Based Systems – Limitations Data dependence  File structure is defined in the program code. Incompatible file formats  Programs are written in different languages, and so cannot easily access each other ’ s files. Fixed Queries/Proliferation of application programs  Programs are written to satisfy particular functions.  Any new requirement needs a new program.

8 DBMS arose as a solution Applications should not need to worry about how data is physically structured and stored Applications should work with a logical data model and declarative query language  Data independence: the single most important reason behind the success of the DBMS today

9 Data Model A collection of concepts/tools for describing conceptual structuring of data (data, data relationships and data constraints). Relational model: the dominating one  Data is stored in relations (basically tables with rows and columns)  Relational database  A Turing Award for E. F. Codd

10 Data Model Others: object-oriented model, object-relational model, etc.  OO model  OO database Schema: a description of data in terms of a data model  it defines the meaning of data

11 Declarative query language Specifies what answers a query should return, but not how the query is executed Leave the implementation details and optimization to DBMS

12 Three-Level Architecture Three levels of data abstractions Need to separate each user ’ s view of the database from its physical representation:  All users should be able to access same data.  Users should not need to know physical database storage details.  A user ’ s view must not be affected by changes made in other users ’ views  Changes to physical storage should not affect database structure or users ’ views

13 Three-Level Architecture

14 Three-Level Architecture: External Level Users ’ view of the database. Describes the part of database that is relevant to a particular user.

15 Three-Level Architecture: Conceptual Level Community view of the database. Describes what data is stored in database and relationships among the data.

16 Three-Level Architecture: Internal Level Physical representation of the database on the computer. Describes how the data is stored in the database.

17 Relating the Three Levels

18 Data Independence Logical Data Independence  Conceptual schema changes should not require changes to external schema, or rewrites of application programs. Physical Data Independence  Internal schema changes (e.g. using different file organizations, storage structures/devices) should not require change to conceptual or external schemas.

19 Data Independence

20 Other DBMS features Besides data independence: Efficient data access Data integrity and security Data administration Concurrency control Crash recovery … Overall: Reduced application development time

21 Major DBMS today Oracle DB2 (IBM) SQL Server (Microsoft) Sybase Informix (acquired by IBM) PostgreSQL (from UC Berkeley’s Ingres, Postgres) MySQL Microsoft Access

22 People and Roles End users  Query/update databases through application user interfaces (e.g., Amazon.com, library catalogues, etc.) Sophisticated users  Those who form requests in database query language Database designers  Design database schema to model aspects of the real world

23 People and Roles Database application developers  Build applications that interface with databases Database administrators (a.k.a. DBA’s)  Load, back up, and restore data, fine-tune databases for performance DBMS developers  Develop the DBMS or specialized data management software, implement new techniques for query processing/optimization inside DBMS

24 After this course At least, you should be a  Sophisticated user  Database designer  Database application developer

25 The learning curve: a sketch How to model real-world data using Entity/Relationship diagram? (Database design) Relational model and how to translate E/R diagrams to the relational model? (Database design) Relational algebra (Theory) SQL (Data query, application development) Normalisation (Database design, also a bit theory)

26 Summary Database management system vs. file-based system Three-level architecture: external, conceptual, internal Data independence: logical, physical People and roles