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= 3 Interface Definition =

3.1 ITI-38 - Cross Gateway Query
This transaction is described in IHE ITI XCA Supplement Section 3.38. The common coding/vocabulary scheme used for the meta-data and query parameters of the Cross Gateway Query is defined in section 3.3 “Query Parameters”.

3.2 Query Parameters
The query parameters for the Cross-Gateway query are defined by the IHE. See Volume 2a of IHE ITI Technical Framework, Section 3.18.4.1.2.3.7 “Parameters for Required Queries”. For more detailed descriptions of the parameters see Volume 3 of the IHE IT Technical Framework, Section 4.1.7 “Document Definition Metadata” Table 4.1-5. Links to these references are provided in Section 1.4 “Referenced Documents and Standards” in this document. Document metadata elements, including coded and non-coded elements, are used in several ways in a document sharing environment such as has been adopted for the NHIN. The primary uses of the metadata are: Each of the metadata elements may contribute to some or all of these uses. In order to allow receiver of the query response to validate patient demographics, the sourcePatientInfo metadata element, although technically optional, should contain a minimum of demographics for the patient, including first name, last name, date of birth, and gender. This is the same requirement as specified by IHE, in the ITI Technical Framework Volume 3 Table 4.1-5 sourcePatientInfo Attribute. HITSP C80 defines value sets for document metadata elements requiring a coded vocabulary term for its value. This specification adopts the vocabulary for document metadata elements defined in HITSP C80[|[1]]. Efficient document searches can best be facilitated by limiting search parameters to a few elements, each with a coarse granularity. For document searches on the NHIN, it is recommended to use the following elements as the primary search parameters:
 * 1) To facilitate efficient searches for documents
 * 2) To provide detailed information that NHIO users can review to determine which documents they wish to retrieve
 * 3) To provide information that computer systems can use to verify that the data is about the correct patient (subset of demographics), determine if they are capable of displaying and/or parsing the document, and to determine if the requesting user has permission to access the document
 * Patient ID
 * Class code
 * Practice Setting Code
 * Healthcare Facility Type
 * Document Creation Time (not a coded element and thus not further described in this document. As referenced above, IHE Technical Framework Volumes 2a and 3 provide more detail for this and other query parameters.)

3.2.1 Patient ID
The Patient ID (PID) is the technical identifier used to represent the subject (patient) for whom documents are sought. This identifier shall originate from an Assigning Authority Domain supporting the NHIO. This specification **//does not//** constrain who the Assigning Authority is, whether it is the same as the Home Community ID, whether more than one might be utilized within an HIO, or whether a given Assigning Authority may be referenced by more than one HIO.

The Patient ID shall contain two parts:
 * Patient Identity Assigning Authority in the form of an OID
 * An identifier in the above Assigning Authority domain

Within the query request and response, these components of the patient ID are to be specified in the HL7 CX format. In the context of an NHIO, these values are exchanged during patient discovery; the Assigning Authority is the //root// of the patient identifier and the Patient ID is the //extension.//

The HL7 identifier type CX consists of several components, but this specification restricts them to the use of two components, the ID Number, and the Assigning Authority (AA). The Assigning Authority identifies the "domain" over which the ID Number represents a unique entity. Furthermore, the AA is represented using a Universal ID and Universal ID Type. In the XDS specification, ISO Object Identifiers must be used as Universal ID. Therefore, Universal ID Type is always ISO. The required format is: IDNumber^^^&OIDofAA&ISO. No other values/modifications in other components or subcomponents are allowed.

An explicit example is: 543797436^^^&1.2.840.113619.6.197&ISO

Note that the '&' character must be properly encoded in the XML content. Within the AdhocQueryRequest, the patient identifier shall be surrounded by single quotes as in the following example:

  'd8420442513945d^^^&amp;1.3.6.1.4.1.21367.2005.1.1&amp;ISO'  

These requirements stem from the IHE specification for the XCA Cross Gateway Query (ITI-38), which bases query parameters on the IHE Registry Stored Query (ITI-18). The Registry Stored Query itself references the XDS document metadata definition and CX data type. These constraints and references are parts of the IHE ITI XCA Supplement Section 3.38.4.1.2.2 and the XDS CX Data Type is described in Volume 3 of the IHE ITI Technical Framework Section 4.1.7 Table 4.1-3.

3.2.2 Hash
The hash contains the hash of the target document, computed following the SHA-1 algorithm. If the hash value is not known at the time of the query, -1 may be returned for the hash value and ‘urn:ihe:iti:2010:StatusType:DeferredCreation’ shall be returned as the DocumentStatus.

3.2.3 Size
The actual size (in bytes) of the document, or -1 if the size of the document is not known at query time. If -1 is specified, ‘urn:ihe:iti:2010:StatusType:DeferredCreation’ shall be returned as the DocumentStatus. **Previous Page---Next Page**

[|[1]] As of October, 2009, a draft of HITSP C80 (v1.1.1) has been produced with significant changes to the section on document metadata, and it is this draft that is being adopted by this specification. It is expected that HITSP will formally adopt and publish these changes sometime in early 2010.