Database Note 1

23 Jul 2018

Database System Concept

key concepts

• Data model
  • set of records, XML,graph
• Schema versus data
• Data definition language set up schema
• Data manipulation or query language for querying and modifying

key people

• DBMS implementer builds system
• Database desinger establishes schema
• Database application developer programs that operate on database: sales database insert/delete
• Database administrator loads the data,keep running smoothly tunning paramer to get better performance highly paid

Relational model

used by all major commercial database systems very simple model query with high-level-languages: simple yet expensive efficient implementations

Relation database

• NULL - special value for ‘unknown” or “undefined”
• key -attribute whose value is unique in each tuple

Querying Relational Database

steps: 1.Design schema;create using DDL 2.’Bulk load’ initial data

1. Repeat: execute queries and modifications

ad-hoc queries in high-level language

Query languages

• relational algebra - formal
• SQL - actual/implemented

XML Data

• Introduction,well-informed XML(extensible markup language)
• well-formed XML adheres to basic structural requirements
• single root element
• matched tags, proper nesting
• unique attributes within elements XML parser(not well-formed)

Document Type Descriptor(DTD)

• grammar-like lauguage
• special attributes types ID and IDREF(S) pointer untyped

DTD/XSD pros:

• Programs can assume structure
• CSS/XSL
• specification - data exchange
• documentation
• benefits of “typing”

cons:

• flexibility, ease of change
• DTDs can be messy – irregular
• XSDs
• benefits of “no typing”