DCIT 55 Advanced Database Management Systems Reviewer: Lecture 1

Database System

• A software system used to store, retrieve, and run queries on data
• A systematic collection of data, which is raw facts or unprocessed data
• The database system provides improved data sharing, data security, data integration, decision making, and end-user productivity

Types of Databases

• Single User Database: supports only one user at a time
• Multi-user Database: supports multiple concurrent users
• Workgroup Database: a multiuser database that supports fewer than 50 users, used for a specific department
• Enterprise Database: represents the overall company data, supporting present and expected future needs
• Centralized Database: stored at a single site
• Distributed Database: stored in two or more physically independent sites
• Cloud Database: created and maintained using cloud services such as Microsoft Azure or Amazon AWS

Data Modeling and Data Model

• Data Modeling: the process of creating a specific data model for a determined problem domain
• Data Model: a representation (usually graphic) of a complex “real-world” data structure

Evolution of Data Models

• Hierarchical Model: uses a hierarchical tree structure to organize the data
• Network Model: a database model conceived as a flexible way of representing objects and their relationships
• Relational Model (Edgar F. Codd): a relational database consists of a collection of tables, each assigned a unique name

Big Data

• Volume: refers to the amounts of data being stored
• Velocity: refers to the speed with which data grows and the need to process it quickly
• Variety: refers to the fact that data is collected in multiple different formats

Database Backup and Recovery

Backup Facilities

• Full Backups: backing up the entire database at a specific point in time
• Incremental Backups: backing up only the data that has changed since the last backup
• Differential Backups: backing up only the data that has changed since the last full backup

Checkpoint Facility

• Allows updates to the database to be made permanent and secure from vulnerability
• Transaction Logs: used to keep track of changes to the database

Recovery Manager

• Allows the database system to restore the database to a reliable and steady-state after any failure
• Point-in-Time Recovery: restoring the database to a specific point in time
• Rollback and Rollforward Operations: undo or redo changes made by incomplete or partially committed transactions
• Crash Recovery: initiates crash recovery procedures to bring the database back to a consistent state

Database Failures

• File Corruption: data corruption in a database file
• File System Damage: damage to the file system that stores the database
• Software and Hardware Failure: failure of software or hardware components that support the database

Problems in Database Systems

• Temporary Update Problem: a scenario where a transaction makes temporary updates to the database and then rolls back those updates
• Incorrect Summary Problem: aggregated or summarized data becomes inaccurate due to updates, deletions, or insertions of individual records
• Lost Update Problem: a concurrency control issue that occurs in multi-user database systems
• Unrepeatable Read Problem: a phenomenon that occurs in database systems with concurrent transactions