dido:public:ra:xapend:xapend.f_qos:presentation
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dido:public:ra:xapend:xapend.f_qos:presentation [2021/06/08 15:23] char |
dido:public:ra:xapend:xapend.f_qos:presentation [2021/10/04 13:40] (current) 50.19.247.197 ↷ Links adapted because of a move operation |
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| ====== F.6 Presentation ====== | ====== F.6 Presentation ====== | ||
| - | [[dido:public:ra:xapend:xapend.f_qos| Return to Quality of Service ]] | + | [[dido:public:ra:xapend:xapend.f_qos:start| Return to DDS Quality of Service ]] |
| - | The PRESENTATION [[dido:public:ra:xapend:xapend.a_glossary:q:qos|QoS]] policy controls the extent to which changes to data-[[ddsf:private:guidebook:06_append:glossary:i:instance|instances]] can be made dependent on each other and also the kind of dependencies that can be propagated and maintained by the Service. | + | The PRESENTATION [[dido:public:ra:xapend:xapend.a_glossary:q:qos|QoS]] [[dido:public:ra:xapend:xapend.a_glossary:p:policy|policy]] controls the extent to which changes to data-[[dido:public:ra:xapend:xapend.a_glossary:i:instance|instances]] can be made dependent on each other and also the kind of dependencies that can be propagated and maintained by the Service. |
| - | The setting of coherent_access controls whether the Service will preserve the groupings of changes made by the publishing application by means of the operations begin_coherent_change and end_coherent_change. | + | The setting of coherent_access controls whether the Service will preserve the groupings of changes made by the publishing [[dido:public:ra:xapend:xapend.a_glossary:a:application|application]] by means of the operations begin_coherent_change and end_coherent_change. |
| The setting of ordered_access controls whether the Service will preserve the order of changes. | The setting of ordered_access controls whether the Service will preserve the order of changes. | ||
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| If coherent_access is set, then the access_scope controls the maximum extent of coherent changes. The behavior is as follows: | If coherent_access is set, then the access_scope controls the maximum extent of coherent changes. The behavior is as follows: | ||
| - | * If ''access_scope'' is set to INSTANCE, the use of ''begin_coherent_change'' and ''end_coherent_change'' has no effect on how the [[ddsf:private:guidebook:06_append:glossary:s:subscriber|subscriber]] can access the data because with the scope limited to each instance, changes to separate instances are considered independent and thus cannot be grouped by a coherent change. | + | * If ''access_scope'' is set to INSTANCE, the use of ''begin_coherent_change'' and ''end_coherent_change'' has no effect on how the [[dido:public:ra:xapend:xapend.a_glossary:s:subscriber|subscriber]] can access the data because with the scope limited to each instance, changes to separate instances are considered independent and thus cannot be grouped by a coherent change. |
| - | * If ''access_scope'' is set to TOPIC, then coherent changes (indicated by their enclosure within calls to ''begin_coherent_change'' and ''end_coherent_change'') will be made available as such to each remote ''DataReader'' independently. That is, changes made to instances within each individual ''DataWriter'' will be available as coherent with respect to other changes to instances in that same ''DataWriter'', but will not be grouped with changes made to instances belonging to a different ''DataWriter''. | + | * If ''access_scope'' is set to [[dido:public:ra:xapend:xapend.a_glossary:t:topic|TOPIC]], then coherent changes (indicated by their enclosure within calls to ''begin_coherent_change'' and ''end_coherent_change'') will be made available as such to each remote ''DataReader'' independently. That is, changes made to instances within each individual ''DataWriter'' will be available as coherent with respect to other changes to instances in that same ''DataWriter'', but will not be grouped with changes made to instances belonging to a different ''DataWriter''. |
| - | * If ''access_scope'' is set to GROUP, then coherent changes made to instances through a ''DataWriter'' attached to a common ''[[ddsf:private:guidebook:06_append:glossary:p:publisher|Publisher]]'' are made available as a unit to remote subscribers. | + | * If ''access_scope'' is set to GROUP, then coherent changes made to instances through a ''DataWriter'' attached to a common ''[[dido:public:ra:xapend:xapend.a_glossary:p:publisher|Publisher]]'' are made available as a unit to remote subscribers. |
| If ''ordered_access'' is set, then the access_scope controls the maximum extent for which order will be preserved by the Service. | If ''ordered_access'' is set, then the access_scope controls the maximum extent for which order will be preserved by the Service. | ||
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| * Finally, if ''access_scope'' is set to GROUP, changes made to instances via ''DataWriter'' entities attached to the same ''Publisher'' object are made available to subscribers on the same order they occur. | * Finally, if ''access_scope'' is set to GROUP, changes made to instances via ''DataWriter'' entities attached to the same ''Publisher'' object are made available to subscribers on the same order they occur. | ||
| - | ; Note | + | ; Note: |
| - | : this QoS policy controls the scope at which related changes are made available to the subscriber. This means the subscriber can access the changes in a coherent manner and in the proper order; however, it does not necessarily imply that the Subscriber will indeed access the changes in the correct order. For that to occur, the application at the subscriber end must use the proper logic in reading the ''DataReader'' objects, as [[ddsf:private:guidebook:06_append:glossary:d:data_distribution_service_dds]] 1.4 Spec, Access to the data. | + | : This QoS policy controls the scope at which related changes are made available to the subscriber. This means the subscriber can access the changes in a coherent manner and in the proper order; however, it does not necessarily imply that the Subscriber will indeed access the changes in the correct order. For that to occur, the application at the subscriber end must use the proper logic in reading the ''DataReader'' objects, as [[dido:public:ra:xapend:xapend.a_glossary:d:dds]] 1.4 Spec, Access to the data. |
dido/public/ra/xapend/xapend.f_qos/presentation.1623180198.txt.gz · Last modified: 2021/06/08 15:23 by char
