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Availability

Availability.

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Availability

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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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