The ClientServer Model LFTSP 1998 IS 6'21

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The Client-Server ModelLFTSP 1998 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

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Distributed Computing
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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

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Host-based processing

• not true client/server computing
• traditional mainframe environment

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

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

Client
Server
Presentation Logic
Application Logic
Database Logic
DBMS
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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
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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
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Examples

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

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Windows NT-style networking
Authentication Client File Client Print
Client Mail Client
Workstations
Authentication Server
File Server
Print Server
Mail Server
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Distributed Database
Database
App
DBMS
Comms
Part of Database
App
App
App
DBMS
Comms
Part of Database
App
App
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CORBA Architecture
http//www.omg.org/
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WWW Architecture
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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.
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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

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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/
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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/
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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

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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

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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

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Typical Display Architecture
Display
Input Devices
Display Manager
Input Manager
Application
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X-Windows Architecture
Display
Input Devices
X-Server
X-Client
Application
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Distributed X-Windows
Application Client
Display
Input Devices
X-Server
X-Client
Application
Application Server
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The Client-Server ModelLFTSP 1998 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