Mission Operations Reference Model. Draft ... - CCSDS

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DRAFT RECOMMENDED PRACTICE FOR MISSION OPERATIONS REFERENCE MODELFor example, the current value of a parameter or the current verification state of atelecommand occurrence is a status attribute. For some types of entities there may bea one-to-one relationship between occurrence and status. For example, an alertoccurrence has no alert status as the occurrence does not change over time. This doesnot violate the relationship, but it must be noted during the specification of therelevant service.e) At any one instant in time there actually exists the following COM relationship:IdentityDefinitionOccurrence1 1 1 n1 1StatusFigure 3-6: COM Live StructureAt any one point in time an entity can have only one active definition, each definitionmay have zero to n occurrences, and each occurrence has only one active status.3.8.2.2 The Definition, Occurrence, and Status components are represented as abstractstructures in the COM. A service specification must extend these abstract structures for it tobe possible to use the COM operations. For example, for telecommands the structures used torepresent the definition, any occurrences, and the evolving status of those occurrences, mustextend the abstract structures defined by the COM formal specification.3.8.3 COMMON OBJECT MODEL UPDATESChanges to the model are communicated to clients by the distribution of updates. The COMdefines a base update message, one for each component of the model, that all service updatesmust extend.a) There exist update structures for Definition, Occurrence, and Status. These structuresextend the basic MAL update structure so that they may be used with thePublish/Subscribe pattern.b) Updates to the COM are either full updates, where a new copy of the item is sent, orpartial, where just an aspect of the item is sent.c) The model defines three complete update messages, one for Definition, one forOccurrence, and one for Status. These shall be used to distribute a complete copy ofthe relevant component. For example, the definition of a new telecommand would besent as a MAL update which would be extended by a complete Definition updatemessage containing the new telecommand Definition structure.d) Partial updates are specified by extending the relevant COM update structure with aservice-specific structure containing the changed information. It is a service specificaspecthow this is defined and what each partial update actually modifies.CCSDS 520.1-R-1 Page 3-19 October 2009
DRAFT RECOMMENDED PRACTICE FOR MISSION OPERATIONS REFERENCE MODEL3.8.4 COMMON MODEL ARCHIVE STRUCTUREServices that utilise the COM must adhere to a basic structure. This structure allows thedefinition of a common archive structure for the provision of historic retrieval and replayservices.As stated in 3.8.2, the Definition, Occurrence, and Status components are represented asabstract structures in the COM. A service specification must extend these abstract structuresfor it to be possible to use the archive and any associated historical services. For example, fortelecommands the structures used to represent the definition, any occurrences, and theevolving status of those occurrences must extend the abstract structures defined in the COMspecification for any COM compliant archive to be able to hold these service-specificstructures:PastDefinitionDefinitionOccurrenceOccurrenceOccurrence1 n1 nStatusStatusStatusStatus1 1 1 n1 1Identity Definition OccurrenceStatusPresentFigure 3-7: COM Historical Archive ModelAs changes are made during the lifetime of the items this information is distributed toconsumers using the COM update structures and the normal MAL interaction patterns. Theseupdates can also be stored in a COM compliant archive:PastDefinitionOccurrenceStatusUpdate messagesIdentityDefinitionOccurrenceStatusPresentDefine/Redefine/Delete Create/Update/Delete UpdateFigure 3-8: Historical Archive UpdatesBy storing these updates in an archive, any historical replay/retrieval operations can correctlyreflect the history of the items.CCSDS 520.1-R-1 Page 3-20 October 2009
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