Modeling the Aspects of Quality of Service in Web Services and ...

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1 < comm_protocol match =“exact”> HTTPS < security_type match = “exact”> SSL < time_scale match = ‘exact”> sec < ta_time match = “max”> 3600 < relative_scale match = “exact”> % < reliability match = “min”> 85 The UDDI upon receiving this message will modify the search by taking the QAs with the highest weights into account. Weights of zero represents informational fields and are used to establish the clear protocol between the SC and the UDDI. Any scale attributes, such as time_scale, would be considered informational and are used to establish the basis for the dialog between the SC and UDDI. Using the “match” field of every attribute, UDDI can narrow the search and better estimate the Quality Value (QV). The “match” field dictates the accuracy of the desired QA. The “match” field can have four different values: • exact – the QA value must match exactly • min – the value given for the QA is the minimum desired value • max – the value given for the QA is the maximum allowed • value unknown – the value for the QA is not known The UDDI will then use the search result to calculate the QV as follows: • For each QA that meets the accuracy requirement, the value of the weight is added to the overall QV. • For each QA that does not meet the accuracy requirement, the value of the weight is subtracted from the overall QV. • The attributes with a weight of zero are used to establish dialog and ensure the scale of comparison of data • The attributes with an unknown value are not considered, and only indicate to the directory that the SC is interested in knowing the value. The values for these attributes indicated unknown are returned with the search results The weights assigned are arbitrarily and relative. The UDDI returns the QV for the services that closely match the required attributes and the SC determines to which SP to connect to. Let us assume initially that the SC has requested the directory to calculate the QV, and return it with the search result. In this case, the following would be returned from the directory as it conforms to figure 2. Acme Search Service B1 175 Acme Search Service B2 205 1 Due to space limitations, we have abbreviated the word quality_attribute with ‘qa’ and the with
Type Attribute Attribute Name Example Application Specific Accuracy of results result_accuracy result_accuracy = 78 weight = 100 Interface requirements interface_grammar interface_grammar = “int int string real” weight = 10 comm_protocol = https weight = 40 Protocol used comm_protocol Security variables: type of security – certificate and the location of the certificate, etc… security_type Session state variables: session timeout, maximum number of session variables allowed, keep alive timeout Time scale Acme Search Service B3 25 In the scenario described above, Acme Services Corp. offers three SES’s, all using the same session_timeout, max_session_var, keep_alive_to time_scale General Value scale value_scale Cost scale Size scale Relative scale Price Turn around time of results Bandwidth requirements Total data to be transmitted Reliability Login Required cost_scale size_scale relative_scale cost_per_usage ta_time bandwidth_req est_data_size reliability req_login Table 1: Quality Attributes and Example Values security_type = SSL weight = 40 session_timeout = 600 max_session_var = 10 keep_alive_to = 30 weight = 10 time_scale = seconds weight = 0 value_scale = real weight = 0 cost_scale = USD weight = 0 size_scale = KB weight = 0 relative_scale = % weight = 0 cost_per_usage = 0.50 weight = 101 ta_time = 360 weight = 90 Bandwidth_req = 256 Weight = 10 est_data_size = 1024 weight = 10 reliability = 99.999 weight = 100 req_login = false weight = 10 algorithm, algorithm B. Based on the QAs desired by the SC, the directory service calculates the (QV) and returns it with the search results. The SC can then determine to which SES it wants to connect to: Acme Search Service B2 in this case. 9. Benefits of QoS In addition to the filtering ability gained during discovery time by the SC in choosing an SP, the SC can cache the returned QVs for later use. In recovery time, the QVs can initially be used to further investigate the possibilities of choosing a backup. The backup and recovery benefits of adding QoS is
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