Web Services

This introduces basic concepts of web services.

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What are Web Services?

Web services are self-contained and self-describing application functionalities that can be processed through open internet standards.

web services ...

• acts like a block box that may require input and deliver a result.
• work on top of any communication technology stack.
• can be published, discovered, and invoked base on open technology standards
• work in synchronous and asynchrounous scenarios
• facilitate integration within an enterprise as well as across enterprises.

Categories of Web Services

Category	Example
Informational	online media (WSJ, CNN), product catalogs (clothing), manuals, white papers, classified ads (eBay, Amazon), online books.
Interactive	registration forms, online games (MSN Gaming).
Transactional	Electronic shopping, ordering goods and services, online banking (citibankonline).
Workflow	Online planning and scheduling systems, inventory management
Collaborative Environments	Distributed authoring systems, Collaborative design tools (photodisc.com).
Web Portals	Electronic infomediaries, electronic shopping malls, search engines, e-mail services (hotmail)

Service Level Agreement (SLA)

SLA statements define expectations for averages and variability in throughput, response time, and availability for each type of customer configuration. Some typical examples:
• While processing a mix of up to 3,000 simultaneous transactions per second:
  • Less than 2 second for 95% of external customers to obtain the application's initial home page coming from broadband connections in the U.S. or
  • less than 4 seconds coming from Citrix dial-up connections.

  • Less than 3 second response time for 95% of all trivial Client/Server transactions against the database server and
    
  • Less than 5 seconds for 95% of all complex Client/Server transactions (such as multi-variable searches and reports).

• Less than 30 seconds to process each email while processing 60,000 e-mail messages per hour.

• 99.9% availability for all services.

Conditions may include all machine also running anti-virus and other background processes.

Different speeds may be allowable during different phases during the development process:

• Five time slower speeds than allowed in production (e.g. 12 seconds) during initial unit test.
• Three times slower speeds than allowed in production during Alpha test.
• Two times slower speeds than allowed in production during Beta test.

Availability (Uptime and Downtime)

Availability percentage	Availability Class (#9's)	Unavailable time per year	Classification
90.0%	1	36.5 days	Unmanaged
99.0%	2	87.6 hours	Managed
99.9%	3	8.8 hours	Well-Managed
99.99%	4	52.6 minutes	Fault-Tolerant
99.999%	5	5.3 minutes	Highly Available
99.9999%	6	31.8 seconds	Very Highly Available
99.99999%	7	3.18 seconds	Ultra Available

The availability of a system or component measures uptime (when a system is available) and downtime (when a system is not available).

A site's perceived availability can be lower than calculated availability if the down time occurs at critical times.

Availability can be improved by either reducing the frequency of failures or by reducing the time to recover from failures.