The ClientServer Model LFTSP 19992000 IS 6.21

1
The Client-Server ModelLFTSP 1999/2000 IS 6.2(1)

• Major Greg Phillips
• Royal Military College of Canada
• Electrical and Computer Engineering
• greg.phillips_at_rmc.ca
• 1-613-541-6000 ext. 6190

2
Distributed Computing
3
Client-Server Computing

• A conceptual implementation model for a software
  system
• Divides the system into
• clients, which request services
• servers, which provide them
• A single process (program) can be simultaneously
  a client or a server

4
Host-based processing

• not true client/server computing
• traditional mainframe environment

Client
Server
Presentation Logic
Application Logic
Database Logic
DBMS
5
Server-based processing

• server does all the processing
• user workstation provides a user-friendly
  interface

Client
Server
Presentation Logic
Application Logic
Database Logic
DBMS
6
Client-based processing

• all application processing may be done at the
  client
• data validation routines and other database logic
  function are done at the server

Client
Server
Presentation Logic
Application Logic
Database Logic
Database Logic
DBMS
7
Cooperative processing

• application processing is performed in an
  optimized fashion
• complex to set up and maintain

Client
Server
Presentation Logic
Application Logic
Application Logic
Database Logic
DBMS
8
Examples

• Windows NT-style networking
• distributed databases
• CORBA
• the World Wide Web
• X-Windows

9
Windows NT-style networking
Authentication Client File Client Print
Client Mail Client
Workstations
Authentication Server
File Server
Print Server
Mail Server
10
Distributed Database
Database
App
DBMS
Comms
Part of Database
App
App
App
DBMS
Comms
Part of Database
App
App
11
CORBA Architecture
http//www.omg.org/
12
WWW Architecture
13
What Makes It Work?

• URL Uniform Resource Locator, a simple scheme
  for locating things
• HTML HyperText Markup Language, a simple
  structural scheme for describing document content
• HTTP HyperText Transfer Protocol, a (fairly)
  simple protocol for moving information from
  servers to clients in response to requests

Standards. Standards make it work.
14
Uniform Resource Identifier

• a single, global namespace for information stored
  on any network in a wide variety of formats
• includes URL (... Location), URC (... Citation)
  and URN (... Name)
• URLs are specified in RFC 1738 (absolute URLs)
  and RFC 1808 (relative URLs)
• general structure is
• scheme//hostport/path/filename
• currently supports http, ftp, gopher, mailto,
  news, and telnet schemes

15
HTML

• HTML is a markup language or encoding formulated
  as an application of SGML (Standard Generalized
  Markup Language), ISO 8879, 1986
• current revision is 4.0, available from the W3C
  (www.w3.org)
• past pattern
• consensus is reached on an HTML standard
• vendors (Microsoft, Netscape) add new,
  incompatible features
• a messy negotiation process ensues
• repeat....

http//www.w3.org/MarkUp/
16
HTTP

• The Hypertext Transfer Protocol (HTTP) is an
  application-level protocol for distributed,
  collaborative, hypermedia information systems. It
  is a generic, stateless, object-oriented protocol
  which can be used for many tasks, such as name
  servers and distributed object management
  systems, through extension of its request
  methods. A feature of HTTP is the typing and
  negotiation of data representation, allowing
  systems to be built independently of the data
  being transferred.

http//www.w3.org/Protocols/
17
Request/Response Structure

• all HTTP communications consist of requests from
  client to server and responses from server to
  client
• a request message from a client to a server
  includes, the method to be applied to the
  resource, the identifier (URI) of the resource,
  the protocol version in use, entity header and
  entity body
• a response consists of a status line, response
  header, entity header, and entity body

18
HTTP Entities

• Entity Header. Defines format and encoding of
  entity body, plus other meta-information
• Encoding. Entity bodies may optionally be
  compressed using either gzip or compress. They
  may also have an associated media type, as
  defined by the MIME standard
• Entity Body. A stream of octets (bytes)
  conforming to the format and encoding specified
  in the Entity Header

19
HTTP Methods

• GET. Return an entity consisting of the
  identified resource
• HEAD. Return only the HEAD portion of the
  identified resource
• POST. Pass the entity to the identified resource
  for action
• PUT. Replace the identified resource with the
  entity
• DELETE. Delete the identified resource
• TRACE. Provide an application layer loop back

20
Typical Display Architecture
Display
Input Devices
Display Manager
Input Manager
Application
21
X-Windows Architecture
Display
Input Devices
X-Server
X-Client
Application
22
Distributed X-Windows
Application Client
Display
Input Devices
X-Server
X-Client
Application
Application Server
23
The Client-Server ModelLFTSP 1999/2000 IS 6.2(1)

• Major Greg Phillips
• Royal Military College of Canada
• Electrical and Computer Engineering
• greg.phillips_at_rmc.ca
• 01-613-541-6000 ext. 6190