Modern Databases - Database Systems - Lecture Slides, Slides of Database Management Systems (DBMS)

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Modern Databases

Other Sorts of DB

• We have looked

mainly at relational

databases

• Relational model
• SQL
• Design techniques
• Transactions
• Many of these topics

relied on relational

concepts

• There are several

other types of DB in

use today

• Distributed DBs
• Object DBs
• Multimedia DBs
• Temporal DBs
• Logic DBs

Client/Server Architecture

• The client/server

architecture is a

general model for

systems where a

service is provided

by one system (the

server) to another

(the client)

• Server
  • Hosts the DBMS and database
  • Stores the data
• Client
  • User programs that use the database
  • Use the server for database access

Distributed Databases

Network

Client(s) Server

Client(s) Server

Client(s) Server

Client(s) Server

Client(s) Server

Web-based Databases

Client

(Browser)

Web

Server

Database

Server

HTTP request

SQL query

SQL result

HTML page

Web-based Databases

• Advantages
  • World-wide access
  • Internet protocols (HTTP, SSL, etc) give uniform access and security
  • Database structure is hidden from clients
  • Uses a familiar interface - Disadvantages - Security can be a problem if you are not careful - Interface is less flexible using standard browsers - Limited interactivity over slow connections

Object Oriented Databases

• An object oriented

database (OODB) is

a collection of

persistent objects

• Objects - instances of a defined class
• Persistent - object exist independently of any program - An object oriented

DBMS

• Manages a collection of objects
• Allows objects to be made persistent
• Permits queries to be made of the objects
• Does all the normal DBMS things as well

OODB example

• In lecture 10 we had

a store with different

sorts of products

• Books
• CDs
• DVDs
• This lead to missing

data among the

various types

• OODB solution
  • We make an abstract Product class
  • Book, CD, and DVD are each a concrete subclass of Product
  • The database is a persistent collection of Products

Object Oriented Databases

• Advantages
  • Good integration with Java, C++, etc
  • Can store complex information
  • Fast to recover whole objects
  • Has the advantages of the (familiar) object paradigm - Disadvantages - There is no underlying theory to match the relational model - Can be more complex and less efficient - OODB queries tend to be procedural, unlike SQL

Object Relational Databases

• Extend a RDBMS

with object concepts

• Data values can be objects of arbitrary complexity
• These objects have inheritance etc.
• You can query the objects as well as the tables - An object relational

database

• Retains most of the structure of the relational model
• Needs extensions to query languages (SQL or relational algebra)

The Information-Integration

Problem

• Related data exists in many places and could, in principle, work together.
• But different databases differ in:
  • Model (relational, object-oriented?).
  • Schema (normalised/ not normalized?).
  • Terminology: are consultants employees? Retirees? Subcontractors?
  • Conventions (meters versus feet?).
• How do we model information residing in heterogeneous sources (if we cannot combine it all in a single new database)?

Example

• Suppose we are integrating information about bars in some town.
• Every bar has a database.
  • One may use a relational DBMS; another keeps the menu in an MS-Word document.
  • One stores the phones of distributors, another does not.
  • One distinguishes ales from other beers, another doesn’t.
  • One counts beer inventory by bottles, another by cases.

Graphs of Semistructured

Data

• Nodes = objects.
• Labels on arcs (attributes, relationships).
• Atomic values at leaf nodes (nodes with no arcs out).
• Flexibility: no restriction on:
  • Labels out of a node.
  • Number of successors with a given label.

Example: Data Graph

Bud

A.B.

1995 Gold

Joe’s Maple

M’lob

beer beer bar manf manf

servedAt

name

name name

addr

prize

year award

root

The bar object for Joe’s Bar

The beer object for Bud

Notice a new kind of data.