Content

1. File System v.s. DBMS
2. Concepts
   1. Data Abstraction
   2. Data Modeling
   3. Database Languages
3. Database Overview

File System v.s. DBMS

• Difficulty in accessing data
• Data redundancy & inconsistency
• Data isolation
• Atomicity problems
• Concurrent access anomalies
• Integrity problem

Concepts

Data Abstraction

Schema: structure (type) Instance: actual content (value)

1. Physical level
   • How data are actually stored
2. Logical level
   • What data are stored
   • Relationship among data
3. View level
   • Part of the entire DB

Data Modeling

Used to describe data in a systematic way.

• Capture user requirements
• Store/access data efficiently
• Describes:
  • Data
  • Data relationships
  • Data semantics
  • Data constraints

Database Languages

• Data Definition Language (DDL)
• Data Manipulation Language (DML)

Database Overview

• Functional components
  • Query processer: high-level user requests -> efficient low-level commands
    • DDL interpreter
      • Interpret DDL statements
      • Definition -> data dictionary
    • DML compiler
      • DML statements -> evaluation plan
      • Query optimization
    • Query evaluation engine
      • Executes low-level instructions generated by DML compiler
  • Storage manager
    • File manager
    • Transaction manager
      • Consistency
    • Authorization & integrity manager
      • Integrity
      • Authority
    • Buffer manager
  • Disk storage
    • Data files
    • Data dictionary: structure, schema
    • Indices: fast access