Types of DataPredefined Data Items:

Numerical/alphabetical items whose meaning and format are specified explicitly.

Common in transaction oriented systemsText:

A series of characters; meaning is not importantImagesAudioVideo

Logical Vs Physical Views of Data

A logical view of data expresses the way a user thinks about the data Usually expressed in terms of a data model.

A physical view of data is the way computers handle the data, i.e., the storage and retrieval of it. Usually stated in terms of specific locations

on storage devices plus techniques used to access it

Data Access Methods

Sequential Access: Individual records within a file are processed in sequence.

Direct Access: The individual item in the file is accessed directly.

Indexed Access: Uses a table(index) to locate the required piece of data. Often called ISAM(Indexed Sequential

Access Method)

Transaction Processing

Logical Reference: Identifies the data that a programmer wants but does not specify how to find the data.

Record Locking: The ability to lock the specific record temporarily to prevent access by any other process until it is unlocked.

Distributed Databases

Databases, parts of which exist in different locations.

Two Phase Commit: A technique used to maintain consistency across the databases.

Database Replication is a common alternative to distributed databases.

Tradeoffs Between Centralized and Distributed Architectures

Cost of data transmission.

Costs of synchronizing distributed parts of the database.

Degree to which the entire database must be current at all times.

Data Warehouse

A large database that is a collection of data from smaller databases.

Used to support decision making.Updated less frequently than say for

example transaction databases.Supports fast online queries and

quick summaries for managers.

Data Warehouse (Contd.)

Global in view.Data mart is a subset of a data

warehouse that provides data about a specific function or a department.

Can “drill down” into several layers of data to locate a problem or an opportunity

Queries are often multidimensional in nature.

Capabilities a good DBMS must possess

Controlling Redundancy Problems with redundancy:

Need for single logical updateWaste of storage spaceInconsistency

Restricting Unauthorized Access Provide a security and authorization

subsystem

Capabilities a good DBMS must possess

Persistent Storage for Program Objects and Data Structures Persistent Objects: Survive the termination of

program execution and can later be directly retrieved.

Cause of emergence of object-oriented DBMS.Database Inferencing Using Deduction

Rules (called deductive database systems)

Capabilities a good DBMS must possess

Providing Multiple User Interfaces.Representing Complex Relationships

among Data.Enforcing Integrity Constraints

Specifying data type for each data item. Specifying that records in one file must

be related to records in other files.Providing Backup and Recovery.

Implications of the Database Approach

Potential for Enforcing StandardsReduced Application Development

TimeFlexibilityAvailability of Up-to-Date InformationEconomies of Scale

Factors Related to Information Usefulness

Information Quality

Information Accessibility

Information Presentation

Issues Related to Information Quality

Accuracy: The extent to which the information represents what it is supposed to represent

Precision: Fineness of detail in the portrayal

Completeness: Extent to which the available information is adequate for the task

Issues Related to Information Quality

Age: Amount of time that has passed since the data were produced.

Timeliness: Extent to which the age of the data is appropriate for the task and the user

Source: The person or organization that produced the data

Issues Related to Information Accessibility

Availability: Extent to which the necessary information exists and can be accessed effectively by people who need it

Admissibility: Whether or not use of the information is legal or culturally appropriate in this situation

Issues Related to Information Presentation

Level of Summarization: Comparison between number of items in the original data and number of items displayed.

Format: Form in which information is displayed to the user.

Issues Related to Information Security

Access Restriction: Procedures and techniques controlling who can access what information under what circumstances.

Encryption: Converting data to a coded from that unauthorized users cannot decode