Circulation interface
The preceding parts of the standard describe how data is transported: as a barcode on the item, as a title record on a data carrier. This part describes something else – how a device talks to the library system while it is running: A patron places a book on the self-checkout unit, the device asks the library system, and the system charges the item.
Who talks to whom#
The interface knows exactly two roles:
| Role | What it is | What it does |
|---|---|---|
| Device | self-checkout unit, return unit, payment station, security gate, account terminal | asks |
| Library system | the library software, or its interface service | answers |
The device asks, the library system answers – never the other way round. Every request receives exactly one response. The library system keeps no session state across requests: Each request carries everything needed to answer it.
Relationship to SIP2#
This interface is not a protocol of its own. It is an application profile of the Standard Interchange Protocol version 2.00 (SIP2), which 3M published in 1997 and released for free use in hardware and software products. Almost every self-service device on the market speaks SIP2; whoever follows this profile can be connected to them.
The standard settles three things SIP2 leaves open:
- which of the sixteen command pairs a device and a library system must support, and which are optional,
- how the identifiers common to the SBC standard – barcode number, accession number, transponder UID – are carried in the fields of the protocol,
- what additional information is exchanged through the extension space SIP2 explicitly provides.
A standard that stands still#
SIP2 dates from 1997; the last edition of its description is dated 11 April 2006. The protocol is no longer being developed – it is now maintained by a committee of the American standards organisation NISO (external site), which long ago published a more extensive successor, NCIP (external site) (ANSI/NISO Z39.83).
For library practice this is no drawback but the very advantage: A standard that no longer moves keeps devices and software working together for years. The devices on the market speak SIP2.
What is not laid down#
The standard describes the exchange of data – not the device and not the library software. It says nothing about what a self-checkout unit looks like, which screens it shows, how it reads RFID tags or which security technology it drives. Nor does it say anything about fee schedules, loan periods or overdue levels: Those are the library's own rules, known and applied by the library system alone.