   
UDT Series on Data Communication Technologies and Standards for Libraries
Models for Open System Protocol Development : A Technical Report (1994)
3. INTERLIBRARY LOAN PROTOCOL (ILL)
Interlibrary loan is performed in various environments. In some countries ILL is a centralized function, in others it may be centralized for one type of library and not for another, in other countries there may be no centralized ILL service at all.
In the ISO 10160 Service Definition three different models for interlibrary loan are described. These three are:
- simple model
- chained model
- partitioned model
These three models for the protocol cover the ways ILLs are performed in different environments. In the description below, the library requesting the ILL is called the Requester, the library that owns the requested document is called the Responder. Any library or service center that interacts in the ILL transaction and is not a Requester or a Responder, whichever role they play, is called an Intermediary.
An ILL transaction is defined in this document as the complete ILL cycle. An ILL transaction may consist of the request of a copy of a document and the delivery of that document; it may consist of the request for a certain document, the negotiations for the loan, the sending of the document and finally the return of the document.
A sub-transaction is the activity between an Intermediary and a possible Responder. The activity is related to the ILL transaction initiated by the Requester.
3.1 Simple Model
In some environments ILL is performed in a decentralized manner. Each library (Requester) has to locate the requested document and send an ILL request. If the owner library does not honour the request (become the Responder), the Requester must then find another library who might own the document and send the ILL request again. This may have to be repeated until a library agrees to become the Responder, or until the Requester gives up.
A special type of the simple model is the use of forwarding of ILL requests. If the receiver of the ILL request does not honour the request, it may be allowed to forward the request to another library. The Requester may even include a list of libraries to which the request may be forwarded. In this model each receiver of the request who forwards the request, will also notify the Requester directly about the forwarding and then close their participation in the transaction. Thus, the ILL request may be sent to a "chain" of systems, but only the system willing to become the Responder will continue the transaction. The ILL transaction is therefore processed with only a Requester and a Responder and follows the simple model.
3.2 Chained Model
A Requester may send an ILL request to another library with "permission to chain". Which means that if the receiver of the request does not, honour the request, it may forward the request to another library or to "the next library on the list" (a list that may be included in the original ILL request). The library forwarding the ILL request will not notify the Requester of the forwarding of the request and replies come back to the requester via the forwarding agency, which becomes and Intermediary. Note that this type of forwarding is not by the use of the Forward service, but by the use of sub-transactions.
In some environments all ILL requests go through an ILL center. The Requester sends the ILL request to the center. The ILL center, now an Intermediary, locates the document and sends the ILL request to the owner library. If the first found owner does not, honour the request, the ILL center will try another owner library. The ILL center continue to try owner libraries until one is willing to become the Responder, or until all possible owners have been tried. If a Responder has been found, the requested document is sent to the ILL center who forwards it to the Requester. All services in the tracking phase, such as recalling, renewal, returning, etc. are all performed via the ILL center.
The ILL center scenario is a combination of a chained and a simple model because the ILL center may send the ILL request to a sequence of libraries (as in the simple model) before a Responder is found. But the links from the Requester to the Responder go through the ILL center (Intermediary) and the ILL center's search for a Responder may consist of many subtransactions of the ILL transaction. The sub-transactions that fail to locate a Responder will be closed and the Requester will generally not be aware of the existence of these sub-transactions. The ILL transaction is therefore performed according to the chained model.
3.3 Partitioned Model
The partitioned model is also a combination of the simple and the chained model. In the partitioned model the Requester, the Intermediaries and the Responder act according to the chained model until a loan has been agreed upon. That is as long as the processing phase lasts. From then on all Intermediaries close their subtransactions and only the Requester and the Responder participate in the rest of the ILL transaction. This usually includes the shipping of the documents and all services connected to the tracking phase such as Reclaim, Renewal, Return, etc.
The partitioned model is used, for instance, in environments where a union catalogue helps locate a Responder, but as soon as a Responder is located, the union catalogue withdraws from the transaction. All communication is then between the Requester and the Responder.
3.4 ILL Services
The services supported in the basic ILL protocol are the following. Through the amendment process the protocol can be augmented to increase functionality, although the basic ILL protocol contains comprehensive services. Section 4 describes amendments in progress.
- ILL-request - Allows a user to request an item from an institution and the Responder to respond, forward or initiate a chain to another Responder.
- Forward - Allows a Responder to forward a request on to another institution selected by the Responder or supplied by the Requester.
- Forward-notification - Allows and Intermediary to notify the Requester that an ILL request has been forwarded and to which Responder.
- Shipped - Allows a Responder to indicate that a requested item has been shipped.
- ILL-answer - Allows a Responder to reply to a request with responses such as the following: conditional, retry, unfilled, locations-provided, will supply, hold places, and estimate.
- Conditional-reply - Allows a Requester to respond with an indication of acceptance or rejection of the imposed conditions when an ILL request is answered with a status of conditional.
- Cancel - Allows a Requester to initiate cancellation of an ILL transaction.
- Cancel-reply - Allows a Responder to accept or refuse a request to cancel an ILL transaction.
- Received - Allows a Requester to indicate that a requested item has been received.
- Recall - Allows a Responder to request that an item be returned immediately.
- Returned -m. Allows a Requester to indicate that a loaned item has been returned to the Responder.
- Checked-in - Allows a Responder to indicate that a loaned item has been returned to the Responder.
- Overdue - Allows a responder to notify the Requester that n item is overdue when the due date for that item is reached.
- Renew - Allows a Requester to request a renewal of a loan.
- Renew-answer - Allows a Responder to accept or refuse a renew request and set a new due date.
- Lost - Allows a Requester to notify the Responder that the item has been lost.
- Damaged - Allows a Requester to notify a Responder that the item is damaged, either by a client or in transit.
- Message - Allows general purpose messaging among ILL transaction participants.
- {SY-query - Allows the Requester to check the status of the ILL transaction on the Responder syste
- Status-or-error-report - Allows the Requester to supply status and/or error information.
- Expiry - Allows the Responder to notify the Requester of the expiration of the ILL transaction.
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