Modern Trends in Databases

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Modern Trends in Databases

• Database Systems Lecture 17

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Last Week

• Today database Security and Integrity
• Aspects of security
• Access to databases
• Making sure the correct data goes in.
• 1) Privileges
• 2) Views
• 3) Integrity constraints

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The Penultimate Lecture

• GOOD Modern Databases
• Distributed DBs
• Web-based DBs
• Multimedia DBs

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Distributed Databases

• Distributed database management system (DDBMS)
• A DBMS (or set of them) to control the databases
• Communication software to handle interaction
  between sites

• A distributed DB system consists of several sites
• Sites are connected by a network
• Each site can hold data and process it
• It shouldnt matter where the data is - the
  system is a single entity

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Types of Distribution

• There are two basic options with which we will be
  concerned when it comes to distribution
• Distributed processing
• Distributed data
• With one exception (distributed data,
  non-distributed processing), neither of these
  necessarily implies the other

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Distributed Processing
New York
London
CLIENT
CLIENT
CLIENT
CLIENT
WIDE AREA NETWORK
CLIENT
CLIENT
CLIENT
CLIENT
Moscow
Beeston
CLIENT
CLIENT
CLIENT
CLIENT
DBMS
CLIENT
CLIENT
CLIENT
CLIENT
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What is a Distributed Database?

• A distributed database system is a collection of
  logically related databases that co-operate in a
  transparent manner.
• There should be location independence
• i.e.- as the user is unaware of where the data is
  located it is possible to move the data from one
  physical location to another without affecting
  the user.

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Distributed Database
New York
London
CLIENT
CLIENT
CLIENT
CLIENT
DBMS
DBMS
WIDE AREA NETWORK
CLIENT
CLIENT
CLIENT
CLIENT
Moscow
Beeston
CLIENT
CLIENT
CLIENT
CLIENT
DBMS
DBMS
CLIENT
CLIENT
CLIENT
CLIENT
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Reasons for Distribution

• Reduced Communication Overhead Most data access
  is local, less expensive and performs better.
• Improved Processing Power Instead of one server
  handling the full database, we now have a
  collection of machines handling the same
  database.
• Removal of Reliance on a Central Site If a
  server fails, then the only part of the system
  that is affected is the relevant local site. The
  rest of the system remains functional and
  available.

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Reasons for Distribution

• Expandability It is easier to accommodate
  increasing the size of the global (logical)
  database.
• Local autonomy The database is brought nearer
  to its users. This can effect a cultural change
  as it allows potentially greater control over
  local data .

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Reasons against Distribution

• Complexity (distributed database systems,
  especially, are considerably more complex than
  centralized or client/server ones)
• Security (more opportunities for protection
  failure or attack)
• Software management costs
• Lack of standards
• Data integrity more difficult to maintain

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Transparency

• To obtain the benefits of distributed data
  without incurring added operational complexity,
  distributed database systems should be
  transparent
• What is transparency?
• A transparent distributed database system would
  look, to a user, just like a centralized database
  system.

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Fragmentation

• When you split data up over separate locations
  you have to make a choice
• Due you split up the rows of a table, or the
  columns of a table?
• These are horizontal and vertical fragmentation
  respectively.

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Horizontal Fragmentation
New York
account_number
branch_name
balance
Hillside Hillside Hillside
A-305 A-226 A-155
500 336 62
Beeston
account_number
branch_name
balance
Valleyview Valleyview Valleyview Valleyview
A-177 A-402 A-408 A-639
205 10000 1123 750
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Vertical Fragmentation
New York
branch_name
tuple_id
customer_name
Lowman Camp Camp Kahn
1 2 3 4
Hillside Hillside Valleyview Valleyview
Beeston
account_number
tuple_id
balance
500 336 205 10000
A-305 A-226 A-177 A-402
1 2 3 4
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Transactions in Distributed Database Systems

• Transactions in a distributed database system may
  be either global or local
• Support for global transactions is provided by
  the DDBMS (Distributed DBMS) in a true
  distributed database system.
• This is not a simple task.

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Distributed vs. centralized

• Both have pros and cons
• In other words, if you choose a distributed
  database you are spreading out lots of small
  headaches rather than having one central migraine.

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TERMINALS
MAINFRAME COMPUTER
NETWORK CONNECTION
PRESENTATION LOGIC
BUSINESS LOGIC
DATA LOGIC
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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

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Client/Server Architecture
SERVER
CLIENT 1
CLIENT 2
DB
DBMS
CLIENT 3
DATA LOGIC
PRESENTATION LOGIC
BUSINESS LOGIC
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Transactions in Client/Server Systems

• Transactions in a single server environment are
  simple the same as in a centralized system
• Transactions in a multi-server system are
  server-oriented.
• That is, a single transaction cannot involve
  multiple servers because the servers operate
  completely independently of each other

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Web-based Databases

• Database access over the internet
• Web-based clients
• Web server
• Database server(s)
• Web server serves pages to browsers (clients) and
  can access database(s)

• Typical operation
• Client sends a request for a page to the web
  server
• Web server sends SQL to database
• The web server uses results to create page
• The page is returned to the client

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Web-based Databases
Client (Browser)
Web Server
DatabaseServer
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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
  extremely careful
• Interface is less flexible using standard
  browsers
• Limited interactivity over slow connections

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Microsoft anyone?
Internet Explorer
ASP .NET
MS SQL Server
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Corporate Style
Internet Explorer
JSP
Oracle
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Open Source
Firefox
PHP
PHP is a scripting language originally designed
for producing dynamic web pages. It has evolved
to include a command line interface capability
and can be used in standalone graphical
applications.
MySQL
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Even more choice-o-rama
Firefox
PHP
Perl
Ruby
Python
Python is an interpreted, object-oriented,
high-level programming language for Rapid
Application Development, as well as for use as a
scripting or glue language to connect existing
components together.
PostgreSQL
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Web Based Approaches

• The scripting language generates the query
  depending on what you the web user requests. It
  then takes the results and formats them into HTML
  Javascript.

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Multimedia Databases

• Multimedia DBs can store complex information
• Images
• Music and audio
• Video and animation
• Full texts of books
• Web pages

• They can be used in a wide range of application
  areas
• Entertainment
• Marketing
• Medical imaging
• Digital publishing
• Geographic Information Systems

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Querying Multimedia DBs

• Metadata searches
• Information about the multimedia data (metadata)
  is stored
• This can be kept in a standard relational
  database and queried normally
• Limited by the amount of metadata avalilable

• Content searches
• The multimedia data is searched directly
• Potential for much more flexible search
• Depends on the type of data being used
• Often difficult to determine what the correct
  results are

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Metadata Searches

• Example - indexing films we might store
• Title
• Year
• Genre(s)
• Actor(s)
• Director(s)
• Producer(s)
• Keywords (!)

• We can then search for things like
• Films starring Kevin Spacey
• Films directed by Peter Jackson
• Dramas produced in 2000
• We dont actually search the films themselves.

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Metadata Searches

• Advantages
• Metadata can be structured in a traditional DBMS
• Metadata is generally concise and so efficient to
  store
• Metadata enriches the content

• Disadvantages
• Metadata cant always be found automatically, and
  so requires data entry
• It restricts the sorts of queries that can be made

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Content Searches

• An alternative to metadata is to search the
  content directly
• Multimedia is less structured than metadata
• It is a richer source of information but harder
  to process

• Example of content based retrieval
• Find images similar to a given sample
• Hum a tune and find out what it is
• Search for features, such as cuts or transitions
  in films

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Content-Based Retrieval
QBIC (Query By Image Content) from IBM -
searches for images having similar colour or
layout
http//wwwqbic.almaden.ibm.com/cgi-bin/stamps-demo
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Content-Based Retrieval

• Image retrieval is hard.
• It is often not clear when two images are
  similar
• Image interpretation is unsolved and expensive
• Different people expect different things

• Do we look for?
• Images of roses
• Images of red things?
• Images of flowers?
• Images of red flowers?
• Images of red roses?