FUNCIONES POR ÁREAS Y DEPARTAMENTOS

Agents can communicate four types of diagnostic information: observations, beliefs, like-lihoods, and dependency knowledge.

Representing observations

Agents express observations using an observation element. The observation has five attributes providing metadata about the observation: an id attribute, a time attribute in-dicating the time the observation was made in milliseconds since Jan 1, 1970 UTC; an originatorattribute indicating the URI of the agent that originally made the observation;

a Booleancachedattribute indicating whether the observation was cached or not; and an expiresattribute indicating the time the information expires in milliseconds since Jan 1, 1970 UTC.

Anobservationelement has exactly one child element, either acomponentelement or atestelement, depending on whether the input component is a network component or a diagnostic test. Thecomponentortestelement has one or moreclasschild elements specifying the class or classes to which the component or test belongs. The content of each class element is a class name. The component or test element may also have zero or more additional child elements describing its properties. Each property is expressed as a child element whose tag name is a property name and whose content is the the value of the prop-erty. For convenience, agents can abbreviate the property name using XML namespaces.

The order of the classes and properties does not matter. The value of descriptive prop-erties is expressed as a string. Leading and trailing whitespace is ignored. The value of relationship properties is expressed as a componentRefchild element. AcomponentRef element has an attributerefwhose value is theidvalue of another component in the com-ponent graph. The metadata in theobservation element applies to all properties in the observation. Below I give an example of an observation of an outbound connectivity test.

<observation id="obs-3"

xmlns:com="http://capri.csail.mit.edu/2006/capri/common#"

time="1168356309119"

originator="http://18.26.0.100/userAgent"

cached="false"

expires="1170451641706">

<test id="test-6">

<class>

http://capri.csail.mit.edu/2006/capri/common#Outbound_Conn_Test

</class>

<com:srcIP> 127.0.0.1 </com:srcIP>

<com:probeURI> capri.csail.mit.edu </com:probeURI>

<com:probeResult> OK </com:probeResult>

<com:localNet> <componentRef ref="com-2"/> </com:localNet>

</test>

</observation>

Representing beliefs

Agents represent beliefs and likelihoods using thebeliefelement. The metadata attributes of a belief element are identical to those of an observation element. A belief has four child elements: a subject indicating the component for which the belief applies, a propertyspecifying the property of the component the belief describes, afromEvidence element listing the evidence used to produce the belief, and either a distribution in-dicating the probability of each of the possible values of the property or a likelihood element indicating the probability of the evidence given each possible value of the prop-erty. The subject element has one child, either a component, test, orcomponentRef element. The format of each of these elements is described above in Section A.2.1. The content of thepropertyelement is the name of the property associated with the belief. The fromEvidenceelement contains zero or more evidence child nodes describing the evi-dence used to infer the belief. If thefromEvidenceelement has noevidencechild nodes, then the belief was inferred using only probabilistic dependency knowledge without any additional evidence. Eachevidence node has a propPath attribute indicating the prop-erty path to a propprop-erty for which the creator of this belief had evidence it used to infer the belief. Thedistributionelement has two or moreentrychild elements. Eachentry el-ement has avalueattribute and apattribute such that P(property=value|evidence) = p.

A likelihood element has the same format, except that for the entry elements for a likelihood, P(evidence|property=value). Below I give an example of a belief about the status of an HTTP Server component inferred from the number of consecutive failures to the server.

<belief id="bel-2"

xmlns:com="http://capri.csail.mit.edu/2006/capri/common#"

originator="http://18.26.0.100:8111/da"

time="1160577157224"

cached="true"

expires="1170451641706">

<subject>

<component id="com-1">

<class>

http://capri.csail.mit.edu/2006/capri/common#HTTP_Server

</class>

<com:hostHash>+0THLqaZnxk9I8bU5ZgDGA==</com:hostHash>

</component>

</subject>

<property>http://capri.csail.mit.edu/2006/capri/core#status</property>

<distribution>

<entry value="OK" p="0.8"/>

<entry value="FAIL" p="0.2"/>

</distribution>

<fromEvidence>

<evidence

propPath="http://capri.csail.mit.edu/2006/capri/common#consecFailuresToServer"

/>

</fromEvidence>

</belief>

Representing dependency knowledge

Agents represent dependency knowledge using the knowledgeelement. Knowledge has the same five metadata attributes as observations and beliefs. A knowledgeelement has three child elements. Thesubjectandpropertychild elements contain the names of the component class and property, respectively, for which the dependency knowledge applies.

Thecptchild specifies the conditional probability table associated with the knowledge. A cptelement has a singleparentschild element containing a whitespace delimited list of parent property paths. The order of the parents matters. A cptelement also has two or moreentrychild nodes. Eachentrychild node has three attributesvalue,parentVals, and psuch that P(property=value|parents=parentVals) =p. The parentVals at-tribute is a whitespace delimited list of parent property values in the order specified in the parentselement. Below I give an example of a piece of dependency knowledge for the asHopTestResultproperty of the AS Hop Test component class.

<knowledge id="knowledge-2"

originator="http://18.26.0.100:8111/da"

time="1160577157224"

cached="false"

expires="1170451641706">

<subject>http://capri.csail.mit.edu/2006/capri/common#AS_Hop_Test</subject>

<property>

http://capri.csail.mit.edu/2006/capri/common#asHopTestResult

</property>

<cpt>

<parents>

http://capri.csail.mit.edu/2006/capri/common#asHop|

http://capri.csail.mit.edu/2006/capri/core#status

</parents>

<entry p=’0.995000’ parentVals=’FAIL’ value=’FAIL’/>

<entry p=’0.020000’ parentVals=’OK’ value=’FAIL’/>

<entry p=’0.005000’ parentVals=’FAIL’ value=’OK’/>

<entry p=’0.980000’ parentVals=’OK’ value=’OK’/>

</cpt>

</knowledge>