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Exploring Service Availability and Accessibility Formulas

Learn about the concepts of service availability and accessibility, compare WSQM and FWSI formulas, and understand key differences and proposed improvements. Discover how these metrics impact overall service quality assessment.

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Exploring Service Availability and Accessibility Formulas

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  1. Availability • 1.1 First, availability is about the presence and ready for immediate use of a service. When we talk about the "presence" of a service two aspects might be considered: location and time. Therefore we have two kinds of availability: in time (e.g. the service is available 24 hours per day) and in space (e.g. the service is available at this location). • What we capture in our definition is just the temporal aspect. • 1.2 In section 5.2.2. in WSQM document, the Availability is defined once as "the average Up Time". However the formula dose not contains any average function. I think this part from the definition "average Up Time" should be removed. • 1.3 Our formula is right but I think the terminology we use is maybe not the best one. I propose to use "measurement_time" instead of "unit time" . • Coming back to the differences between WSQM and FWSI availability formulas, I don’t understand why in FWSI formula they relate to the number of invocations. A closer look at the availability and accessibility (here I consider the slides available at: • http://www.oasis-open.org/apps/org/workgroup/wsqm/download.php/17560/QoS- • WSQM-Analysis-03.ppt) • in FWSI shows that these two are basically the same: (1) Availability = Number of successful invocations/Total invocations and (2) Accessibility = Successful invocations/Total invocations. • I think that WSQM describes better temporal availability in a given period of time. However if we think about a set of periods of time then we need some average functions on availabilities to measure the overall availability. Ioan Toma

  2. Accessibility • . Accessibility as it is defined in WSQM document is fine. • The formulas for accessibility in WSQM and FWSI in my opinion are the same. FWSI just impose the restriction that invocations are fired simultaneously and therefore the answer to "*Can we deduce that the FWSI formula is a sub-set of WSQM formula?" question is "yes". WSQM formula dose not impose such a restriction and thus applies also when invocations are fired simultaneous or not. Ioan Toma

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