org.omg.dds.core.policy

Interface Presentation

All Superinterfaces:

Comparable<Presentation>, DDSObject, QosPolicy, QosPolicy.ForPublisher, QosPolicy.ForSubscriber, RequestedOffered<Presentation>, Serializable

public interface Presentation
extends QosPolicy.ForPublisher, QosPolicy.ForSubscriber, RequestedOffered<Presentation>

Specifies how the samples representing changes to data instances are presented to the subscribing application. This policy affects the application's ability to specify and receive coherent changes and to see the relative order of changes. The accessScope determines the largest scope spanning the entities for which the order and coherency of changes can be preserved. The two booleans control whether coherent access and ordered access are supported within the scope accessScope. Concerns: Publisher, Subscriber RxO: Yes Changeable: No This QoS policy controls the extent to which changes to data 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 coherentAccess controls whether the Service will preserve the groupings of changes made by the publishing application by means of the operations Publisher.beginCoherentChanges() and Publisher.endCoherentChanges(). The setting of orderedAccess controls whether the Service will preserve the order of changes. The granularity is controlled by the setting of the accessScope. Note that 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. The value offered is considered compatible with the value requested if and only if the following conditions are met:

1. The inequality "offered access_scope >= requested access_scope" evaluates to true. For the purposes of this inequality, the values of Presentation.AccessScopeKind are considered ordered such that INSTANCE < TOPIC < GROUP.
2. Requested coherentAccess is false, or else both offered and requested coherentAccess are true.
3. Requested orderedAccess is false, or else both offered and requested orderedAccess are true.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	Presentation.AccessScopeKind

Nested classes/interfaces inherited from interface org.omg.dds.core.policy.QosPolicy

QosPolicy.ForDataReader, QosPolicy.ForDataWriter, QosPolicy.ForDomainParticipant, QosPolicy.ForDomainParticipantFactory, QosPolicy.ForPublisher, QosPolicy.ForSubscriber, QosPolicy.ForTopic

Method Summary

Methods

Modifier and Type	Method and Description
Presentation.AccessScopeKind	getAccessScope()
boolean	isCoherentAccess() If coherentAccess is set, then the accessScope controls the maximum extent of coherent changes.
boolean	isOrderedAccess() If orderedAccess is set, then the accessScope controls the maximum extent for which order will be preserved by the Service.
Presentation	withAccessScope(Presentation.AccessScopeKind accessScope) Copy this policy and override the value of the property.
Presentation	withCoherentAccess(boolean coherentAccess) Copy this policy and override the value of the property.
Presentation	withGroup()
Presentation	withInstance()
Presentation	withOrderedAccess(boolean orderedAccess) Copy this policy and override the value of the property.
Presentation	withTopic()

Methods inherited from interface org.omg.dds.core.DDSObject

getEnvironment

Methods inherited from interface org.omg.dds.core.policy.RequestedOffered

requestedOfferedContract

Methods inherited from interface java.lang.Comparable

compareTo

Method Detail

getAccessScope

Presentation.AccessScopeKind getAccessScope()

Returns:

the accessScope

isCoherentAccess

boolean isCoherentAccess()

If coherentAccess is set, then the accessScope controls the maximum extent of coherent changes. The behavior is as follows:

• If accessAcope is set to Presentation.AccessScopeKind.INSTANCE, the use of Publisher.beginCoherentChanges() and Publisher.endCoherentChanges() has no effect on how the 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 accessScope is set to Presentation.AccessScopeKind.TOPIC, then coherent changes (indicated by their enclosure within calls to Publisher.beginCoherentChanges() and Publisher.endCoherentChanges()) 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 accessScope is set to Presentation.AccessScopeKind.GROUP, then coherent changes made to instances through a DataWriter attached to a common Publisher are made available as a unit to remote subscribers.

See Also:

getAccessScope()

isOrderedAccess

boolean isOrderedAccess()

If orderedAccess is set, then the accessScope controls the maximum extent for which order will be preserved by the Service.

• If accessScope is set to Presentation.AccessScopeKind.INSTANCE (the lowest level), then changes to each instance are considered unordered relative to changes to any other instance. That means that changes (creations, deletions, modifications) made to two instances are not necessarily seen in the order they occur. This is the case even if it is the same application thread making the changes using the same DataWriter.
• If accessScope is set to Presentation.AccessScopeKind.TOPIC, changes (creations, deletions, modifications) made by a single DataWriter are made available to subscribers in the same order they occur. Changes made to instances through different DataWriter entities are not necessarily seen in the order they occur. This is the case, even if the changes are made by a single application thread using DataWriter objects attached to the same Publisher.
• Finally, if accessScope is set to Presentation.AccessScopeKind.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.

See Also:

getAccessScope()

withAccessScope

Presentation withAccessScope(Presentation.AccessScopeKind accessScope)

Copy this policy and override the value of the property.

Returns:

a new policy

withCoherentAccess

Presentation withCoherentAccess(boolean coherentAccess)

Copy this policy and override the value of the property.

Returns:

a new policy

withOrderedAccess

Presentation withOrderedAccess(boolean orderedAccess)

Copy this policy and override the value of the property.

Returns:

a new policy

withInstance

Presentation withInstance()

withTopic

Presentation withTopic()

withGroup

Presentation withGroup()