org.omg.CosNotifyFilter
Interface FilterOperations

All Known Subinterfaces:

Filter

public interface FilterOperations

The Filter interface defines the behaviors supported by objects which encapsulate constraints used by the proxy objects associated with an event channel in order to determine which events they receive will be forwarded, and which will be discarded.

Each object supporting the Filter interface can encapsulate a sequence of any number of constraints. Each event received by a proxy object which has one or more objects supporting the Filter interface associated with it must satisfy at least one of the constraints associated with one of its associated Filter objects in order to be forwarded (either to another proxy object or to the consumer, depending on the type of proxy the filter is associated with), otherwise it will be discarded.

Each constraint encapsulated by a filter object is a structure comprised of two main components. The first component is a sequence of data structures, each of which indicates an event type comprised of a domain and a type name. The second component is a boolean expression over the properties of an event, expressed in some constraint grammar (more on this below). For a given constraint, the sequence of event type structures in the first component nominates a set of event types to which the constraint expression in the second component applies. Each element of the sequence can contain strings which will be matched for equality against the domain_name and type_name fields of each event being evaluated by the filter object, or it could contain strings with wildcard symbols (*), indicating a pattern match should be performed against the type contained in each event, rather than a comparison for equality when determining if the boolean expression should be applied to the event, or the event should simply be discarded without even attempting to apply the boolean expression. Note that an empty sequence included as the first component of a constraint implies that the associated expression applies to all types of events, as does a sequence comprised of a single element whose domain and type name are both set to either the empty string or else the wildcard symbol alone contained in quotes.

The constraint expressions associated with a particular object supporting the Filter interface are expressed as strings which obey the syntax of a particular constraint grammar (i.e., a BNF). Implementations may support other constraint grammars, and/or users of this service may implement their own filter objects which allow constraints to be expressed in terms of an alternative constraint grammar. As long as such user-defined filter objects support the Filter interface, they can be attached to Proxy or Admin objects in the same fashion as the default Filter objects supported by the implementation of the service are, and the channel should be able to use them to filter events in the same fashion.

The Filter interface supports the operations required to manage the constraints associated with an object instance which supports the interface, along with a readonly attribute which identifies the particular constraint grammar in which the constraints encapsulated by this object have meaning. In addition, the Filter interface supports three variants of the match operation which can be invoked by an associated proxy object upon receipt of an event (the specific variant selected depends upon whether the event is received in the form of an Any, a Structured Event, or a Typed Event), to determine if the event should be forwarded or discarded, based on whether or not the event satisfies at least one criteria encapsulated by the filter object.

The Filter interface also supports operations which enable a client to associate with the target filter object any number of callbacks, which are notified each time there is a change to the list of event types, which the constraints encapsulated by the filter object could potentially cause proxies to which the filter is attached to receive. Operations are also defined to support administration of this callback list by unique identifier.

The operations supported by the Filter interface are described in more detail within the following subsections.

Method Summary

ConstraintInfo[]	add_constraints(ConstraintExp[] constraint_list) The add_constraints operation is invoked by a client in order to associate one or more new constraints with the target filter object.
int	attach_callback(NotifySubscribe callback) This operation is invoked to associate with the target filter object an object supporting the CosNotifyComm::NotifySubscribe interface.
java.lang.String	constraint_grammar() The constraint_grammar attribute is a readonly attribute which identifies the particular grammar within which the constraint expressions encapsulated by the target filter object have meaning.
void	destroy() The destroy operation destroys the target filter object, invalidating its object reference.
void	detach_callback(int callback) After this method is called, the callback object to which the input value corresponds is removed from the list of those associated with the target filter object, so that subsequent changes to the event type subscription list encapsulated by the target filter object will not be propagated to the callback object which is being detached.
ConstraintInfo[]	get_all_constraints()
int[]	get_callbacks()
ConstraintInfo[]	get_constraints(int[] id_list) The get_constraints operation is invoked to return a sequence of a subset of the constraints associated with the target filter object.
boolean	match_structured(StructuredEvent filterable_data) The match_structured operation evaluates the filter constraints associated with the target filter object against an instance of an event supplied to the channel in the form of a Structured Event.
boolean	match_typed(Property[] filterable_data) The match operation evaluates the filter constraints associated with the target filter object against an instance of an event supplied to the channel in the form of a typed event.
boolean	match(Any filterable_data) The match operation evaluates the filter constraints associated with the target filter object against an instance of an event supplied to the channel in the form of a CORBA::Any.
void	modify_constraints(int[] del_list, ConstraintInfo[] modify_list) The modify_constraints operation is invoked by a client in order to modify the constraints associated with the target filter object.
void	remove_all_constraints() The remove_all_constraints operation is invoked to remove all of the constraints currently encapsulated by the target filter object.

Method Detail

get_callbacks

int[] get_callbacks()

Returns:

The sequence of all unique identifiers associated with callback objects attached to the target filter object.

detach_callback

void detach_callback(int callback)
                     throws CallbackNotFound

After this method is called, the callback object to which the input value corresponds is removed from the list of those associated with the target filter object, so that subsequent changes to the event type subscription list encapsulated by the target filter object will not be propagated to the callback object which is being detached.

Parameters:

A - numeric value which should be one of the unique identifiers associated with one of the callback objects attached to the target filter object.

Throws:

CallbackNotFound - If the input value does not correspond to the unique identifier of a callback object currently attached to the target filter object.

attach_callback

int attach_callback(NotifySubscribe callback)

This operation is invoked to associate with the target filter object an object supporting the CosNotifyComm::NotifySubscribe interface. This interface is inherited by all supplier interfaces (either those that are clients of a notification channel, or those that are proxy objects within a notification channel) defined by the Notification Service, and supports a subscription_change operation. After this operation has been successfully invoked on a filter object, each time the set of constraints associated with the target filter object is modified (either by an invocation of its add_constraints or its modify_constraints operations), the filter object will invoke the subscription_change object of all its associated callback objects in order to inform suppliers to which the target filter object is attached of the change in the set of event types to which clients of the filter object subscribe. This enables suppliers to make intelligent decisions about which types of events it should actually produce, and which it can suppress the production of.

Parameters:

callback - The reference to an object supporting the CosNotifyComm::NotifySubscribe interface.

Returns:

A numeric value assigned to this callback that is unique to all such callbacks currently associated with the target object.

match_typed

boolean match_typed(Property[] filterable_data)
                    throws UnsupportedFilterableData

The match operation evaluates the filter constraints associated with the target filter object against an instance of an event supplied to the channel in the form of a typed event.

The act of determining whether or not a given event passes a given filter constraint is specific to the type of grammar in which the filter constraint is specified. Thus, this operation will need to be re-implemented for each supported grammar.

Parameters:

filterable_data - A sequence of name-value pairs which contains the contents of the event to be evaluated.

Returns:

A boolean value which will be TRUE in cases where the input event satisfies one of the filter constraints, and FALSE otherwise.

Throws:

UnsupportedFilterableData - If the input parameter contains data that the match operation is not designed to handle. An example of this would be if the filterable data contained a field whose name corresponds to a standard event field that has a numeric value, but the actual value associated with this field name within the event is a string.

match_structured

boolean match_structured(StructuredEvent filterable_data)
                         throws UnsupportedFilterableData

The match_structured operation evaluates the filter constraints associated with the target filter object against an instance of an event supplied to the channel in the form of a Structured Event.

The act of determining whether or not a given event passes a given filter constraint is specific to the type of grammar in which the filter constraint is specified. Thus, this operation will need to be reimplemented for each supported grammar.

Parameters:

filterable_data - A data structure of type CosNotification::StructuredEvent, which contains an event to be evaluated.

Returns:

A boolean value which will be TRUE in cases where the input event satisfies one of the filter constraints, and FALSE otherwise.

Throws:

UnsupportedFilterableData - If the input parameter contains data that the match operation is not designed to handle. An example of this would be if the filterable data contained a field whose name corresponds to a standard event field that has a numeric value, but the actual value associated with this field name within the event is a string.

match

boolean match(Any filterable_data)
              throws UnsupportedFilterableData

The match operation evaluates the filter constraints associated with the target filter object against an instance of an event supplied to the channel in the form of a CORBA::Any.

The act of determining whether or not a given event passes a given filter constraint is specific to the type of grammar in which the filter constraint is specified. Thus, this operation will need to be re-implemented for each supported grammar.

Parameters:

filterable_data - A CORBA::Any which contains an event to be evaluated.

Returns:

A boolean value which will be TRUE in cases where the input event satisfies one of the filter constraints, and FALSE otherwise.

Throws:

UnsupportedFilterableData - If the input parameter contains data that the match operation is not designed to handle. An example of this would be if the filterable data contained a field whose name corresponds to a standard event field that has a numeric value, but the actual value associated with this field name within the event is a string.

destroy

void destroy()

The destroy operation destroys the target filter object, invalidating its object reference.

remove_all_constraints

void remove_all_constraints()

The remove_all_constraints operation is invoked to remove all of the constraints currently encapsulated by the target filter object. Upon completion, the target filter object will still exist but have no constraints associated with it.

get_all_constraints

ConstraintInfo[] get_all_constraints()

Returns:

A sequence of structures, each of which contains one of the constraints encapsulated by the target object along with its associated unique identifier.

get_constraints

ConstraintInfo[] get_constraints(int[] id_list)
                                 throws ConstraintNotFound

The get_constraints operation is invoked to return a sequence of a subset of the constraints associated with the target filter object.

Parameters:

id_list - A sequence of numeric values, which should correspond to the unique identifiers of constraints encapsulated by the target object.

Returns:

A sequence of data structures, each of which contains one of the input identifiers along with its associated constraint.

Throws:

ConstraintNotFound - If one of the input values does not correspond to the identifier of some encapsulated constraint. This exception contains as data the numeric value that did not correspond to some constraint.

modify_constraints

void modify_constraints(int[] del_list,
                        ConstraintInfo[] modify_list)
                        throws InvalidConstraint,
                               ConstraintNotFound

The modify_constraints operation is invoked by a client in order to modify the constraints associated with the target filter object. This operation can be used both to remove constraints currently associated with the target filter object, and to modify the constraint expressions of constraints which have previously been added to the target filter object.

Note that the semantics of the modify_constraints operation are such that its side effects are performed atomically upon the target filter object. Once modify_constraints is invoked by a client, the target filter object is temporarily disabled from usage by any proxy object it may be associated with. The operation is then carried out, either successfully deleting all of the constraints identified in the first input sequence and modifying those associated with constraints identified in the second input sequence, or performing no side effects to the target object (in the case one of the inputs was invalid). Upon completion of the operation, the target filter object is effectively re-enabled and can once again be used by associated filter objects in order to make event forwarding decisions.

Parameters:

del_list - A sequence of numeric values which are each intended to be the unique identifier associated with one of the constraints currently encapsulated by the target filter object. If all input values supplied within a particular invocation of this operation are valid, then the specific constraints identified by the values contained in the first input parameter will be deleted from the list of those encapsulated by this target filter object.

modify_list - A sequence of structures, each of which contains a constraint structure and a numeric value. The numeric value contained by each element of the sequence is intended to be the unique identifier associated with one of the constraints currently encapsulated by this target filter object. If all input values supplied within a particular invocation of this operation are valid, then the constraint expression associated with the already encapsulated constraint identified by the numeric value contained within each element of the input sequence will be modified to the new constraint expression that is contained within the same sequence element.

Throws:

ConstraintNotFound - If any of the numeric values supplied within either of the two input sequences does not correspond to the unique identifier associated with some constraint currently encapsulated by the target filter object. This exception contains as data the specific identifier, which was supplied as input but did not correspond to the identifier of some constraint encapsulated by the target object.

InvalidConstraint - If any of the constraint expressions supplied within an element of the second input sequence is not a valid expression in terms of the constraint grammar supported by the target object. This exception contains as data the specific constraint that was determined to be invalid.

add_constraints

ConstraintInfo[] add_constraints(ConstraintExp[] constraint_list)
                                 throws InvalidConstraint

The add_constraints operation is invoked by a client in order to associate one or more new constraints with the target filter object. Upon processing each constraint, this target object associates a numeric identifier with the constraint that is unique among all constraints it encapsulates.

Note that the semantics of the add_constraints operation are such that its sideeffects are performed atomically upon the target filter object. Once add_constraints is invoked by a client, the target filter object is temporarily disabled from usage by any proxy object it may be associated with. The operation is then carried out, either successfully adding all of the input constraints to the target object or none of them (in the case one of the input expressions was invalid). Upon completion of the operation, the target filter object is effectively re-enabled and can once again be used by associated filter objects in order to make event forwarding decisions.

Parameters:

constraint_list - A sequence of constraint data structures, each element of which consists of a sequence of event type structures and a constraint expressed within the constraint grammar supported by the target object.

Returns:

A sequence in which each element will be a structure including one of the input constraint expressions, along with the unique identifier assigned to it by the target filter object.

Throws:

InvalidConstraint - If any of the constraints in the input sequence is not a valid expression within the supported constraint grammar. This exception contains as data the specific constraint expression that was determined to be invalid.

constraint_grammar

java.lang.String constraint_grammar()

The constraint_grammar attribute is a readonly attribute which identifies the particular grammar within which the constraint expressions encapsulated by the target filter object have meaning. The value of this attribute is set upon creation of a filter object instance, based on the input provided to the factory creation operation for the filter instance. The dependency of a filter object on its constraints being expressed within a particular constraint grammar manifests itself within the implementation of the match operations described below, which must be able to parse the constraints to determine whether or not a particular event satisfies one of them. Every conformant implementation of the Notification Service must support an implementation of the Filter interface which supports the default constraint grammar. Thevalue which the constraint_grammar attribute is set to in the case the target filter object supports this default grammar will be EXTENDED_TCL. In addition, implementations and/or end users may provide additional implementations of the Filter interface which support different constraint grammars, and thus would set the constraint_grammar attribute to a different value upon creation of such a filter object.