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This chapter provides an overview of databases and database management systems (dbms). It explains what a database is, the advantages and disadvantages of using a database approach, fundamental database concepts, dbms roles, data definition, field types, queries and reports, data dictionary, data integrity, data security, and databases and the web.
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Database: a collection of related data stored in a manner so it can be retrieved selectively
Database management system (DBMS): the software used to create, modify, and access databases
DBMSs available for PCs include: Microsoft Access (most widely used) Lotus Approach Enterprise-level DBMSs include: Oracle (the market leader) IBM DB MySQL
Use databases, not just "regular" files for all data processing Using regular files is the file processing approach
Advantages:
Better information Faster response time Lower operating costs and storage requirements Improved data integrity and better data management
Disadvantages: Higher software cost Increased vulnerability (backup is essential)
A database consists of one or more tables
Each table contains information for one type of person, place, or thing, e.g., the Car table contains information for all cars
A table consists of one or more records Each record contains information for one person, place or thing, e.g., record 5 in the Car table contains the information for car
A record consists of one or more fields Each field contains one unit of information for that person, place, thing, e.g., the Color field contains the color for that car
Table demo
Users: use the DBMS to enter data, update data, write queries, and generate reports
Database designers: design databases
Define fields and rules for them
Database developers: create the databases
Use the DBMS and a programming language
Database programmers: write the programs to process information
Use the DBMS and a programming language
Database administrators: manage database security, access, and backup and restore
Data definition: the process of describing the characteristics of fields
Must be done for every field of every table
Each field must have:
Name (must be unique within the table) Data type (such as Text, Number, Currency, or Date) Properties, including: Field size (number of characters or bytes) Range of permitted values (number fields) Default value (initial value of the field) Format when printed, e.g., number of decimal places for a number
Text: contains text, such as name and address
Alphabetic: contains only letters, e.g., "hello: Alphanumeric: contains letters and numbers, e.g., "abc123"
Number: contains a number such as a age
Date: contains a date Many possible date formats The unambiguous date format is dd-mon-yyyy
Currency: contains a currency number Has units such as dollars or Euros
Several other types common (^) Fields demo
A query selects records and fields from one or more tables and displays the selections
For example, select all records for "John Smith" You specify the criteria to be matched, e.g., the value of the name field must be "John Smith" Can have multiple criteria, e.g., "John Smith" and year "2000" You specify the fields to be displayed for each matching record
A report selects records and fields from one or more tables and prints the selections
Similar to query except printed in a format you select
Query demo
Alphabetic/numeric check: tests whether the correct type of characters are entered
Range check: tests whether the entered number is in the acceptable range Numeric fields only
Completeness check: tests whether the entry is complete, e.g., has entered a complete SSN
Consistency check: tests whether the entry is consistent with other data, e.g., if state is Illinois, country must be U.S.A.
Data security: protecting data against destruction and misuse
Prevents access from unauthorized individuals
Required to maintain data privacy
Protects against data loss
Protects against intentional and accidental problems
Requires backup and recovery procedures
Disaster recovery plan: what to do if all databases are lost and must restore from scratch
Requires full offsite backup
Databases are commonly used on the Web for:
Information retrieval Dynamic Web pages (change based on user input) E-commerce
