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The Database Environment Lecture 1

 

The database environment • To be able to function, an organisation needs information, e.g. list of books in a library, customer details in a retail business, specifications of cars and their components for a car manufacturer

• Information may be defined as data represented in a meaningful form. Same data shown in different ways will provide different information to different viewers • A major requirement of any computer system is to store and retrieve data in a way that is meaningful to the end  – so user –  user so the core of any Information System is data, which is to be transformed into information through data

modelling  

Definitions • Data: Meaningful facts, text, graphics, images, sound, video segments. • Database: An organized collection of logically related data. • Information: Data processed to be useful in decision making. • Metadata: Data that describes data.

 

Data in Context

 

Summarized data

 

Disadvantages of file processing systems Still widely used today (e.g. for backup) but have the following problems: • Program-Data Dependence (see Fig.) – file descriptions are stored within each application that accesses file, so change to file structure requires changes to all file descriptions in all programs. • Data Redundancy (Duplication of data) – wasteful, inconsistent, loss of metadata integrity (same data has different names in different files, or same name may be used for different data in different files). • Limited Data Sharing – users have little opportunity to share data outside their own applications. • Lengthy Development Times – little opportunity to re-use previous development efforts. • Excessive Program Maintenance – factors above combine to create heavy maintenance load

 

Advantages of the database approach • Minimal Data Redundancy/Improved Consistency • Data Integration • Multiple Relationships

 

Database management system • A DBMS is a data storage stora ge and retrieval system which permits data to be stored non-redundantly non-redundan tly while making it appear to the user as if the data is well-integrated.

 

Advantages of the database approach • Data Independence/Reduced Maintenance • Improved Data Sharing • Increased Application Development Productivity • Enforcement of Standards

• Improved Data Quality (Constraints) • Better Data Accessibility/ Responsiveness • Security, Backup/Recovery, Concurrency

 

Costs and risks of the database approach • New, Specialized Personnel required • Installation Management Cost and Complexity • Conversion Costs • Need for Explicit Backup and Recovery

• Organizational Conflict

 

Pine valley furniture company • We will be using this fictitious company as a case study • The The co comp mpan any’s y’s ffir irst st st step ep w was as to ccre reat atee an E Ent nter erpri prise se Dat Dataa Model (a model of the organisation that provides valuable information about how the organisation functions, function s, as well as important constraints – it stresses the integration of data and processes by focussing on entities, relationships and business rules) • First make a list of all the high-level activities that support business activities

 

Pine valley furniture company • Enterprise data model is a graphical model that shows the th e high-level entities and the associations among them (see Fig.): An ENTITY-RELATIONSHIP DIAGRAM. • The three associations (relationships) are shown by lines connecting the entities • Each CUSTOMER places any number of ORDERS (conversely, each ORDER is placed by exactly one CUSTOMER) • Each ORDER contains any number of ORDER LINEs (conversely, each ORDER LINE is contained in exactly one ORDER)

 

Tables • Relational databases views all data in the form of tables t ables • Following Figs. a and b shows four tables, Customer, Product, Order and OrderLine (the 4 entities shown in the previous ER diagram).

• Each column represents an attribute, e.g. the Customer table has attributes ID, Name, Address..etc. • Relationships between entities are represented by values stored in columns of the corresponding tables, e.g. Customer_ID is an attribute of both the Customer table and the Order table. This makes it easy to link an order with its customer.

 

Fig. (a) Order and Order_Line tables

 

Fig. (b) Product and Customer tables

 

The range of  database applications •

Personal Database PCs/PDAs, Cellphones – OK in special situations where need to share data amongst users is unlikely to arise

•

Workgroup Database. Designed to support collaboration in a small team (less than 25 people)

•

Department Database typically larger than a workgroup (25-100 people) and more diverse range of functions – e.g. personnel database

•

Enterprise Database – scope of the whole organisation. May be more than one, as a single database for a large organisation may be impractical due to performance difficulties for large databases, diverse needs of user groups, and difficulty of achieving common definition of  data (metadata) for all users.

 

Workgroup database with local area network

 

An enterprise data warehouse

 

Components of the database environment • CASE Tools –  Tools – automated automated tools used to design databases and applications • Repository –  Repository – generalised generalised knowledge for all data definitions, relationships, screen/report formats –  formats – an an extended set of metadata for managing databases and other components of the information system • (sometimes Database Management (DBMS) (DBMS) –   – software software specialised System hardware) used to define, create, maintain and provide controlled access to the database and the repository. • Database  – an Database –  an organised collection of logically related data occurrences

 

Components of the database environment • Application Programs – software used to create and maintain the database and provide information to users. • User Interface –  Interface – languages, languages, menus etc by which users interact with other system components

• Data Administrators – people responsible for overall information resources of an organisation. • Systems analysts/programmers and end Users –  Users – people people who add, delete and modify the database and who get information from it.

 

Evolution of  database systems • 1960’s –   file file processing systems: punch cards, paper tape, magnetic tape – sequential access and batch processing • 1970s - Hierarchical and Network (legacy, some still used  – difficulties today) –  today) difficulties = hard to access data (navigational record-at-a-time procedures), limited data independence, no widely accepted theoretical model (unlike relational) • 1980s - Relational –  Relational  – E.F. E.F. Codd and others this  – all theoretically well-founded model model –  all datadeveloped represented in the form of tables –  tables – Oracle, Oracle, DB2, Ingres • 1990s - Object-oriented, but some organisations have to handle large amounts of both structured and unstructured data, so Object-relational databases developed.

 

Evolution of database systems • 2000 and beyond – multi – tier, tier, client-server, distributed environments, web-based, contentaddressable storage, data mining

 

SQL Is: • Structured Query Language (some for historical reasons call it ‘Sequel’  • The standard and most common language for relational database management systems • An SQL-based relational database application involves a user interface, a set of tables in the database, and a RDBMS with an SQL capability • Within the RDBMS SQL will be used to create the tables, translate user requests, maintain the data dictionary and system catalog, update an maintain

the establish security, and carry out backup andtables, recovery procedures  

The SQL environment

• Following Fig. Shows a schematic of an SQL environment • Each database is contained in a catalog, which describes any object that is part of the database (regardless of which user created that object). Most companies keep at least two versions of any database they are using. PROD_C is the live production version, which captures real business data and this must be very tightly controlled and monitored. DEV_C is the development version used when the database is being built and continues to serve as a development tool where enhancements and maintenance efforts can be tested before application to the production database. • Each database will have a set of schemas associated with a

catalog. • Schema = the structure that contains descriptions of objects created by a user (base tables, views, constraints)  

  A simplified schematic of a typical SQL environment

 

3 types of SQL commands • 1. Data Definition Language (DDL) commands - that define a database, including creating, altering, and dropping tables and establishing constraints • 2. Data Manipulation Language (DML) commands co mmands - that maintain and query a database • 3. Data Control Language (DCL) commands - that control a database, including administering privileges and committing data

 

SQL Data types • CHAR(n) –  CHAR(n) fixed-length data, n characters long Maximum – fixed-length length = 2000 character bytes  – variable • VARCHAR2(n) (n) –  variable length character data, maximum 4000 bytes • LONG –  LONG – variable-length variable-length character data, up to 4GB. Maximum 1 per table • NUMBER(p,q) – general purpose numeric data type • INTEGER(p)  – signed INTEGER(p) –  signed integer, p digits wide • FLOAT(p) –  FLOAT(p) – floating floating point in scientific notation with p binary digits precision • DATE – fixed-length date/time in dd-mm-yy form

 

Syntax used in these notes • Capitals = command syntax (may not be required by the RDBMS) • Lowercase = values that must be supplied by user • Brackets = enclose optional syntax • Ellipses (...) = indicate that the accompanying syntactic clause may be repeated as necessary • Each Each SQ SQL L ccom omma mand nd ends ends wi with th a ssem emic icol olon on ‘; ‘;’’ 

• In interactive mode, when the user presses the RETURN key, the SQL command will execute

 

SQL Database Definition • Data Definition Language (DDL) has these major CREATE statements:  –  CREATE SCHEMA –  SCHEMA – defines defines a portion of the database owned particular user. Schemas are dependent catalogby anda contain schema objects, including base on a tables and views, domains, constraints, assertions, character sets, collations etc.  –  CREATE TABLE –  TABLE – defines defines a new table and its columns. The table may be a base table or a derived table. Tables are dependent on a schema. Derived tables are created by executing a query that uses one or more tables or views.

 

SQL Database Definition • CREATE VIEW – defines a logical table from one or more tables or views. There are limitations on updating data through a view. Where views can be updated, those changes can be transferred to the underlying base tables originally referenced to create the view.

 

SQL database definition • Each of the previous create commands may be reversed using a DROP command, so DROP TABLE will destroy a table (including its definitions, contents and any schemas or views associated with it) • Usually only the table creator may delete the table • DROP SCHEMA and DROP VIEW will also delete the named schema or view. • ALTER TABLE may be used to change chan ge the definition of  an existing table

 

Creating tables • Once data model is designed and normalised, the columns needed for each table can be defined using the CREATE TABLE command. The syntax for this is shown in the following Fig. These are the seven steps to follow: • 1. Identify the appropriate datatype for each , including length and precision • 2. Identify those columns that should accept null values. Column controls that indicate a column cannot be null are established when a table is created and are enforced for every update of the table

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Creating tables • 3. Identify those columns that need to be UNQUE - when the data in that column must have a different value (no duplicates) for each row of data within that table. Where a column or set of columns is designated as UNIQUE, this is a candidate key. Only one candidate key may be designated as a PRIMARY KEY • 4. Identify all primary key-foreign key mates. Foreign keys can be established immediately or later by altering the table. The parent table in such a parent-child relationship should be created first. The column constraint

REFERENCES can be used to enforce referential re ferential integrity  

Creating tables • 5. Determine values to be inserted into any columns for which a DEFAULT value is desired - can be used to define a value that is automatically inserted when no value is provided during data entry. • 6. Identify any columns for which domain specifications may be stated that are more constrained than those established by data type. Using CHECK it is possible to establish validation rules for values to be inserted in serted into the database • 7. Create the table and any desired indexes using the

CREATE TABLE and CREATE INDEX statements  

Table creation General syntax for CREATE TABLE

 

Table creation • The following Fig. Shows SQL database definition commands • Here some additional column constraints are shown, and primary and foreign keys are given names

• For examp example, le, the CUS CUSTOM TOMER ER tab table’s le’s pri prima mary ry key is CUSTOMER_ID • The primary key constraint is named CUSTOMER_PK, without the constraint name a system identifier would be assigned automatically and the identifier would be difficult