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Object IdentifiersThe basic YAZ representation of an OID is an array of integers, terminated with the value -1. The ODR module provides two utility-functions to create and copy this type of data elements:
Odr_oid *odr_getoidbystr(ODR o, char *str); |
Creates an OID based on a string-based representation using dots (.) to separate elements in the OID.
Odr_oid *odr_oiddup(ODR odr, Odr_oid *o); |
Creates a copy of the OID referenced by the o parameter. Both functions take an ODR stream as parameter. This stream is used to allocate memory for the data elements, which is released on a subsequent call to odr_reset() on that stream.
The OID module provides a higher-level representation of the family of object identifiers which describe the Z39.50 protocol and its related objects. The definition of the module interface is given in the oid.h file.
The interface is mainly based on the oident structure. The definition of this structure looks like this:
typedef struct oident { oid_proto proto; oid_class oclass; oid_value value; int oidsuffix[OID_SIZE]; char *desc; } oident; |
The proto field takes one of the values
PROTO_Z3950 PROTO_SR |
If you don't care about talking to SR-based implementations (few exist, and they may become fewer still if and when the ISO SR and ANSI Z39.50 documents are merged into a single standard), you can ignore this field on incoming packages, and always set it to PROTO_Z3950 for outgoing packages.
The oclass field takes one of the values
CLASS_APPCTX CLASS_ABSYN CLASS_ATTSET CLASS_TRANSYN CLASS_DIAGSET CLASS_RECSYN CLASS_RESFORM CLASS_ACCFORM CLASS_EXTSERV CLASS_USERINFO CLASS_ELEMSPEC CLASS_VARSET CLASS_SCHEMA CLASS_TAGSET CLASS_GENERAL |
corresponding to the OID classes defined by the Z39.50 standard. Finally, the value field takes one of the values
VAL_APDU VAL_BER VAL_BASIC_CTX VAL_BIB1 VAL_EXP1 VAL_EXT1 VAL_CCL1 VAL_GILS VAL_WAIS VAL_STAS VAL_DIAG1 VAL_ISO2709 VAL_UNIMARC VAL_INTERMARC VAL_CCF VAL_USMARC VAL_UKMARC VAL_NORMARC VAL_LIBRISMARC VAL_DANMARC VAL_FINMARC VAL_MAB VAL_CANMARC VAL_SBN VAL_PICAMARC VAL_AUSMARC VAL_IBERMARC VAL_EXPLAIN VAL_SUTRS VAL_OPAC VAL_SUMMARY VAL_GRS0 VAL_GRS1 VAL_EXTENDED VAL_RESOURCE1 VAL_RESOURCE2 VAL_PROMPT1 VAL_DES1 VAL_KRB1 VAL_PRESSET VAL_PQUERY VAL_PCQUERY VAL_ITEMORDER VAL_DBUPDATE VAL_EXPORTSPEC VAL_EXPORTINV VAL_NONE VAL_SETM VAL_SETG VAL_VAR1 VAL_ESPEC1 |
again, corresponding to the specific OIDs defined by the standard.
The desc field contains a brief, mnemonic name for the OID in question.
The function
struct oident *oid_getentbyoid(int *o); |
takes as argument an OID, and returns a pointer to a static area containing an oident structure. You typically use this function when you receive a PDU containing an OID, and you wish to branch out depending on the specific OID value.
The function
int *oid_ent_to_oid(struct oident *ent, int *dst); |
Takes as argument an oident structure - in which the proto, oclass/, and value fields are assumed to be set correctly - and returns a pointer to a the buffer as given by dst containing the base representation of the corresponding OID. The function returns NULL and the array dst is unchanged if a mapping couldn't place. The array dst should be at least of size OID_SIZE.
The oid_ent_to_oid() function can be used whenever you need to prepare a PDU containing one or more OIDs. The separation of the protocol element from the remainder of the OID-description makes it simple to write applications that can communicate with either Z39.50 or OSI SR-based applications.
The function
oid_value oid_getvalbyname(const char *name); |
takes as argument a mnemonic OID name, and returns the /value field of the first entry in the database that contains the given name in its desc field.
Finally, the module provides the following utility functions, whose meaning should be obvious:
void oid_oidcpy(int *t, int *s); void oid_oidcat(int *t, int *s); int oid_oidcmp(int *o1, int *o2); int oid_oidlen(int *o); |
Note: The OID module has been criticized - and perhaps rightly so - for needlessly abstracting the representation of OIDs. Other toolkits use a simple string-representation of OIDs with good results. In practice, we have found the interface comfortable and quick to work with, and it is a simple matter (for what it's worth) to create applications compatible with both ISO SR and Z39.50. Finally, the use of the /oident database is by no means mandatory. You can easily create your own system for representing OIDs, as long as it is compatible with the low-level integer-array representation of the ODR module.