History of Implementation Data Models

Databases were:

• Early Business Computer Systems– Accounting functions - payroll, profit/loss

statements

• Files of data - file oriented (physical hardware)– sequential and random access (index)

In 1960's needed:

• Integrated centralized data structure

• Redundancy

• DBA's

• Data models

Mid 1960's - Hierarchical data model •  logical level - data relationships

• relationships structured as hierarchies

• parents and children

• child can have only 1 parent

• 1-to-many

Hierarchical Example

department customer

Employee project invoice store

dep super worker invoice_line contact

Hierarchical DB

• Used pointers

• Any query through the data followed pointers

• manipulated 1 row at a time

• how about many-to-many relationships?

• Problems?

Late 1960's - Network Model

•  many-to-many relationships

•  more than 1 parent

• Owner-Member Relationship

• Instances or Occurrences

•   Problems?

Network example

Sales rep customer

invoice store

invoice _line contact

1970's Relational Model - E.F. Codd •  Rows and Columns

• Instead of 1 record at a time, files or sets at a time

• Easier to write queries

• Limitations?

Relational example

Customer:

CID storeID contact Invoice#

Sales Rep:

SRID Invoice # InvoiceLine

1980's Object-Oriented DBs

•  Represent real-world entities as objects– Objects and relationships– Classes and instances– Specialization /Generalization– Inheritance, methods

• Similar to hierarchical

• Most versions based on relational

• Problems?

1990’s – Extend Relational

• Object-Relational DBs – Keep relational, but add OO features

• Additional Issues:– Distributed DBs – Data mining and data warehouses– Real-time Databases

2000’s – Recent Issues

• Data integration

• Database Security

• Web Databases & Information Retrieval

• XML Databases

• Mobile Databases

• Sensor Databases

• Data-intensive computing (Data Grids)

• Cloud computing - where do databases fit in?