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3.2.11 Termination Facility
The Termination Facility consists of the single service, Close.
18.104.22.168 Close Service
The Close service allows either an origin or target to abruptly terminate all active operations and to initiate termination of the Z-association.
The Close service may be used only when version 3 is in force. If so, following initialization, at any time until a Close request is either issued or received, either the origin or target:
Table 15: Parameters of the Close Service
|Diagnostic-information||x (opt.)||x (opt.)|
|Resource-report-format||x (opt.)||Origin only|
|Resource-report||x (opt.)||x (opt.)||Target only|
|Other-information||x (opt.)||x (opt.)|
|Reference-id||x (if appl.)||x (if appl.)|
22.214.171.124.1 Close-reason This parameter indicates the reason why the origin or target is closing the Z-association. Its values are:
Note: Both the Close request and Close response map to the same protocol message (Close APDU). If both systems issue a Close request at the same time, each will receive the peer message as a Close response (even though the message was not sent as such). This potential ambiguity will not effect the correct operation of the protocol. However, for the case where the message is indeed sent as a Close response, the last of the above listed statuses, "response to Close request" is provided and may optionally be used.
126.96.36.199.2 Diagnostic-information The target may include an optional text message, providing additional diagnostic information.
188.8.131.52.3 Resource-report-format and Resource-report When the origin issues a Close request: the origin may include the parameter resource-report-format to request that the target include a resource report (see 184.108.40.206.1) in the response. The target's decision to include a resource report in the response (and the format) is unilateral: it may include or omit a report regardless of whether the origin included the parameter resource-report-format.
When the target issues a Close request: the target may unilaterally include a resource report.
220.127.116.11.4 Other-information This parameter may be used by the origin or target for additional information, not specified by the standard.
18.104.22.168.5 Reference-id The parameter Reference-id may be included or omitted on a Close request or response from the origin.
The target should omit Reference-id on a Close request. On a Close response, if the target is responding to a Close request that included Reference-id, the target may either include Reference-id using the identical value, or it may omit the parameter. If the target is responding to a Close request that did not include a Reference-id, the target should omit the parameter.
3.3 Message/Record Size and Segmentation
A "segment" is a message that is sent (or is in preparation for transmission) by the target as part of an aggregate Present response, i.e., a Segment request or Present response.
Throughout 3.3, "record" is used as follows:
Except within 3.3.3, a set of records is said to "fit in a segment" if the sum of their sizes, not including protocol control information, does not exceed Preferred-message-size. For the Present operation, the target might be unable to fit the requested records in a single segment, because of record or message size limitations. In that case, the target may perform segmentation of the Present response (if segmentation is in effect) by sending multiple segments (Segment requests followed by Present response).
Two levels of segmentation, level 1 and level 2, are subject to negotiation. If neither level is in effect, the target response to a Present request consists of a simple Present response (a single segment) which contains an integral number of records. If level 1 segmentation is in effect, the target response to a Present request may consist of multiple segments (Segment requests followed by a Present response), and each segment must contain an integral number of records, i.e., records may not span segments. If level 2 segmentation is in effect, the target response to a Present request may consist of multiple segments, and records may span segments.
3.3.1 Procedures When No Segmentation
is in Effect
The procedures in this section (3.3.1) apply when no segmentation is in effect. (They apply not only to a Present operation when no segmentation is in effect, but they also apply in general to a Search operation, whether or not segmentation is in effect; a Search response is not subject to segmentation.)
The target responds to a Present request with a simple Present response (or to a Search request with a Search response), which contains an integral number of records. If the target is not able to return all of the records requested, because of message size limitations, the target should fit as many records as possible.
Assume that the target is attempting to return records M through N. If records M through N fit in the response, then the target returns those records. Otherwise, the target returns records M through P, where P is chosen such that records M through P fit in the response, but records M through P+1 do not.
Assume that the target is attempting to return records 1 through 10; records 1 through 6 fit in the response, but retrieval records 1 through 7 will not fit.
The size of retrieval record 7, itself:
(a) does not exceed Preferred-message-size, or
(b) exceeds Preferred-message-size, but does not exceed Exceptional-record-size, or
(c) exceeds Exceptional-record-size.
In case (a), the target returns records 1 through 6. In case (b), except as noted below (see "Exception"), the target substitutes a diagnostic record for retrieval record 7, indicating that the record exceeds Preferred-message-size. In case (c) the target substitutes a diagnostic record for retrieval record 7, indicating that the record exceeds Exceptional-record-size. (If Exceptional-record-size equals Preferred-message-size then there is no distinction between the meaning of the two diagnostics.)
In case (b) or (c):
If a Present request specifies a single record (i.e. Number-of-records-requested equals 1) then if the size of that retrieval record exceeds Preferred-message-size, but does not exceed Exceptional-record-size, the target will return that single retrieval record. Note that this exception applies only to a Present operation and not to a Search operation.
Thus in case (b), the origin may subsequently retrieve retrieval record 7, by issuing a Present request in which that record is the only record requested.
Note that the purpose of this distinction between Preferred-message-size and Exceptional-record-size is to allow the transfer of normal length records to proceed in a routine fashion with convenient buffer sizes, while also providing for the transfer of an occasional exceptionally large retrieval record without requiring the origin to continually allocate and hold local buffer space for worst-case records. Note also that this intended purpose is defeated if the origin routinely requests a single record.
3.3.2 Level 1 Segmentation
When level 1 segmentation is in effect, the target may segment the aggregate Present response into multiple segments (zero or more Segment requests followed by a Present response), each consisting of integral records (i.e. records may not span segments). The procedures described in this section (3.3.2) apply if level 1 segmentation is in effect.
Beginning with the first record requested and continuing with adjacent higher number records, the target forms segments to contain the requested records. Each segment is sent as a Segment request, except the last, which is sent as a Present response.
The number of segments must not exceed the value of the (optional) Present request parameter Max-segment-count, if supplied.
If Max-segment-count is supplied, and its value is 1, then the procedures of 3.3.1 apply. Also, the same exception as cited in 3.3.1 applies if a Present request has requested a single record.
Assume that the origin requests result set records M through N.
Case A: M<N (i.e. more than one record requested).
Case B: M=N (i.e. a single record requested). The target sends a simple Present response (a single segment). The size of the segment may exceed Preferred-message-size. The segment contains the single requested retrieval record, or a surrogate diagnostic record if the size of the record exceeds Exceptional-record-size.
Assume the origin has requested records 1 through 10.
Present-status is 'partial-2' (not all expected response records available, because they will not all fit within the preferred message size).
3.3.3 Level 2 Segmentation
When level 2 segmentation is in effect, the target may segment the aggregate Present response into multiple segments (as is the case for level 1 segmentation) and in addition, records may span segments. The procedures described in this section (3.3.3) apply if level 2 segmentation is in effect.
If a retrieval record will not fit in a segment (along with records already packed into the segment) it may be segmented into multiple contiguous fragments (see 22.214.171.124) to be packed into consecutive segments according to the procedures detailed in 126.96.36.199 and 188.8.131.52.
A fragment is a proper substring of a record (as noted above, within section 3.3.3 a record is treated as a string of bytes). A particular instance of segmentation of a record results in a sequence of two or more fragments whose concatenation (not including protocol control information) is identical to the record. However, there may be different instances of segmentation of a particular record, a nd the origin cannot necessarily predict how a record will be segmented into fragments by the target in a particular instance.
For the purpose of procedure description (184.108.40.206) a starting fragment is defined to be a fragment that starts at the beginning of a record. An intermediate fragment is a fragment that neither starts at the beginning nor ends at the end of a record. A final fragment is a fragment that ends at the end of a record. An integral record (not segmented) is not a fragment.
The sum of the sizes of the records and record fragments in a segment, not including protocol control information, must not exceed Max-segment-size (see 220.127.116.11).
18.104.22.168 Segment Size, Record Size, and Segment
If level 2 segmentation is in effect, the Present request may optionally include these three parameters:
Max-segment-size -- The largest allowable segment. If included, overrides Preferred-message-size (for this Present operation only). If not included, Max-segment-size assumes the value Preferred-message-size.
Max-record-size -- The largest allowable retrieval record within the aggregate Present response. If included, it must equal or exceed Max-segment-size. (If level 2 segmentation is in effect, the parameter Exceptional-record-size that was negotiated during initialization does not apply, whether or not Max-record-size is included, unless the value of Max-segment-count is 1.)
Max-segment-count -- The maximum number of segments the target may include in the aggregate Present response. If its value is 1, no segmentation is applied for the operation, the procedures of section 3.3.1 apply, and Max-record-size should not be included.
If the latter two parameters are both included, Max-record-size must not exceed the product Max-segment-size times Max-segment-count.
If Max-record-size but not Max-segment-count is included, the origin should be prepared to receive as many segments as necessary to retrieve the requested records.
If Max-segment-count is included (and its value is greater than 1), but Max-record-size is not, the product Max-segment-size times Max-segment-count is the maximum record size for the operation.
If the latter two parameters are both omitted the origin should be prepared to receive arbitrarily large records and an arbitrary number of segments.
22.214.171.124 Segmentation Procedures
The following procedures apply for level 2 segmentation. The target fits as many integral records as possible into the first segment. If all of the requested records will fit, the segment is sent as a simple Present response. Otherwise, in the space remaining within that segment the target fits a starting fragment of the following record (if possible), and the segment is sent as a Segment request. The target then fits the remainder of that record into the next segment (if possible; and if not possible, sends Segment requests as necessary with intermediate fragments, and fits the final fragment, if any, into the beginning of the next segment) and fills as many integral records as possible within the space remaining within that segment. If the last of the requested records is placed in the segment (or Max-segment-count is reached) the segment is sent as a Present response. Otherwise the target continues to fill segments in this manner until the last of the requested records is placed in a segment or Max-segment-count is reached, and sends each segment as a Segment request except the last, which it sends as a Present response. These procedures are re-iterated more formally as follows:
Assume that the origin requests records M through N. (Note that "Record" means "surrogate diagnostic record" if the size of the record exceeds Max-record-size, or if the target is unable to segment the record so that each fragment fits within a segment.)
Assume the origin has requested records 1 through 12. All records are 500 bytes, except record 5, which is 10,000 bytes. Max-segment-size is 3200.
Any message sent from origin to target or vice versa (i.e. any request or response defined by this service definition) is part of an operation (identified by its Reference-id), with the following exceptions:
This standard does not assume any relationship between a given operation and any subsequent operation even if the latter operation uses the same reference-id. This standard does not specify the contents of the Reference-id parameter, nor its meaning, except to the extent that it is used to refer to an operation. Reference-ids are always assigned by the origin and have meaning only within the origin system. Since no semantics are attributed to the Reference-id, it has no implied data type and can only be described as transparent binary data. (Its ASN.1 type is therefore OCTET STRING.)
3.5 Concurrent Operations
If 'concurrent operations' is in effect, the Reference-id parameter is mandatory in an initiating request (however, see note), and the origin may initiate multiple concurrent operations, each identified by a different reference-id.
Note: The Reference-id parameter is always optional in an Init request; 'concurrent operations' does not take effect until negotiation is complete, and is thus not in effect during an Init operation.
Once an operation is initiated, until that operation is terminated, another operation may not be initiated with the same reference-id. This standard does not specify the order in which concurrent operations are processed at the target; the target may process concurrent operations in any manner it chooses.
the origin may issue a Search request using Reference-id "100," and then issue a second Search request using Reference-id "101" before receiving the Search response from the first Search request. There would then be two concurrent operations. Receipt by the origin of the response corresponding to the second Search request (identified by Reference-id "101") would terminate the second operation, and that might occur before termination of the first operation (identified by Reference-id "100"). The origin might then issue a Present request (against the result set created by the second operation), initiating another operation. In that case, the origin must supply a Reference-id other than "100" (because there is an active operation with that Reference-id). The new Reference-id could (but need not) be "101"; if it is, the target may not assume any implied relationship between this new operation and the previous operation which used Reference-id "101."
No operation may be initiated while an Init operation is in progress. No operation may be initiated within a Z-association after a Close request has been sent or received.
All result sets are, in principle, available to any operation. It is possible that two or more concurrent operations will attempt to reference the same result set. This standard does not specify what happens in that circumstance. The origin should not initiate concurrent Search operations with the same value of Result-set-id.
Other than the restriction cited above (that when the origin uses a Reference-id to initiate an operation, until that operation is terminated it may not use that Reference-id to initiate another operation) there are no restrictions on the re-use or management of Reference-ids by the origin. The origin might re-cycle Reference-ids randomly among users, or it may manage local threads by assigning different Reference-ids to end-users. The target is not required to know how the origin manages Reference-ids, or in particular, that the origin is using Reference-ids to distinguish different users. There is no requirement for the target to have any knowledge of multiple end users at the origin, the target interacts only with the (single) origin.
3.6 Composition Specification
For each database supported the target defines one or more schemas (see 3.1.5), and designates one as the default schema. For each schema, the target designates one or more element specification identifiers.
An element specification identifier is the object identifier of an element specification format (a structure used to express an element specification) or an element set name. The latter is a primitive name. An element specification is an instance of an element specification format, or an element set name.
For the default schema, at least one of the element specification identifiers must be an element set name, and the target designates one as the default element set name for the database.
Note: the target designates this information either via the Explain facility, or through some mechanism outside of the standard.
For each record to be returned in a Search or aggregate Present response, the target applies an abstract record structure (defined by a schema for the database to which that record belongs) to form an abstract database record, to which the target applies an element specification to form another instance of the abstract database record (the latter might be a null transformation), to which the target applies a record syntax, to form a retrieval record.
If the origin includes the parameter Comp-spec (in a Present request) the procedures of 3.6.1 apply. For a Search operation, or a Present operation when the parameter Comp-spec is omitted, the default schema is assumed for each record, and the procedures of 3.6.2 apply.
3.6.1 Comp-spec Specified
The Present request parameter Comp-spec includes a set of one or more pairs of a database name and associated composition specification. Each composition specification may include a schema identifier (or if not, the default schema for the database is assumed) and an element specification. For each record to be returned in the aggregate Present response:
The parameter Comp-spec may alternatively consist of a single composition specification with no database specified. In that case, for each record to be returned, if the target is able to form an abstract database record according to that composition specification, it does so. If not, an abstract database record is composed according to the default schema and default element set name for the database to which the record belongs.
The target applies a record syntax (which may be included in the composition specification or within the parameter Preferred-record-syntax) to the resulting abstract database record, to form a retrieval record.
3.6.2 Comp-spec Omitted
When requesting the retrieval of a set of records from a result set, if the parameter Comp-spec is omitted, the procedures of this section apply. Notes:
The Search request parameters Small-set-element-set-names and Medium-set-element-set-names, and the Present request parameter Element-set-names, take the form of a set of one or more pairs of a database name and associated element set name. For each record to be returned in the Search or aggregate Present response, the target first applies the abstract record structure defined by the default schema for the database to which the record belongs, to form an abstract database record, and then applies an element set name, as follows:
If the database to which the record belongs is specified (as a component of one of the pairs), and if the corresponding element set name is valid for the default schema for the database, then the target applies that element set name.
If not, the target applies the default element set name for the database.
Each of these parameters may alternatively consist of a single element set name with no database specified. In that case, for each record to be returned, if the element set name is valid for the default schema for the database to which the record belongs, the target applies that element set name; if not, the target applies the default element set name for the database.
A target must always recognize the character string "F" as an element set name to mean "full"; when it is applied to an abstract database record, it results in the same abstract database record (i.e. a null transformation).
A target must always recognize the character string "B" as an element set name to mean "brief" record. This standard does not define the meaning of "brief." Unless the origin knows the target's definition of "brief" for a given schema, it should not assume that any particular elements are included.
The origin may specify a "preferred-record-syntax," which the target applies (to the abstract database record formed by the application of the element set name) to form a retrieval record. If the origin does not specify a preferred-record-syntax the target may select one (see 126.96.36.199.5).
3.6.3 Record Syntax
For each record to be returned in a Search or aggregate Present response, the element set name, or the schema and element specification from the composition specification, results in an abstract database record, as described above. To that abstract database record, the target applies a record syntax, indicated as described above. The term "record syntax" has the following meaning: