The basic YAZ representation of an OID is an array of integers,
terminated with the value -1. This integer is of type
Odr_oid.
Fundamental OID operations and the type Odr_oid
are defined in yaz/oid_util.h.
An OID can either be declared as a automatic variable or it can
allocated using the memory utilities or ODR/NMEM. It's
guaranteed that an OID can fit in OID_SIZE integers.
Example 9.13. Create OID on stack
We can create an OID for the Bib-1 attribute set with:
Odr_oid bib1[OID_SIZE];
bib1[0] = 1;
bib1[1] = 2;
bib1[2] = 840;
bib1[3] = 10003;
bib1[4] = 3;
bib1[5] = 1;
bib1[6] = -1;
And OID may also be filled from a string-based representation using dots (.). This is achieved by function
int oid_dotstring_to_oid(const char *name, Odr_oid *oid);
This functions returns 0 if name could be converted; -1 otherwise.
Example 9.14. Using oid_oiddotstring_to_oid
We can fill the Bib-1 attribute set OID easier with:
Odr_oid bib1[OID_SIZE];
oid_oiddotstring_to_oid("1.2.840.10003.3.1", bib1);
We can also allocate an OID dynamically on a ODR stream with:
Odr_oid *odr_getoidbystr(ODR o, const char *str);
This creates an OID from string-based representation using dots.
This function 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.
Example 9.15. Using odr_getoidbystr
We can create a OID for the Bib-1 attribute set with:
Odr_oid *bib1 = odr_getoidbystr(odr, "1.2.840.10003.3.1");
The function
char *oid_oid_to_dotstring(const Odr_oid *oid, char *oidbuf)
does the reverse of oid_oiddotstring_to_oid. It
converts an OID to the string-based representation using dots.
The supplied char buffer oidbuf holds the resulting
string and must be at least OID_STR_MAX in size.
OIDs can be copied with oid_oidcpy which takes
two OID lists as arguments. Alternativly, an OID copy can be allocated
on a ODR stream with:
Odr_oid *odr_oiddup(ODR odr, const Odr_oid *o);
OIDs can be compared with oid_oidcmp which returns
zero if the two OIDs provided are identical; non-zero otherwise.
From YAZ version 3 and later, the oident system has been replaced by an OID database. OID database is a misnomer .. the old odient system was also a database.
The OID database is really just a map between named Object Identifiers (string) and their OID raw equivalents. Most operations either convert from string to OID or other way around.
Unfortunately, whenever we supply a string we must also specify the
OID class. The class is necessary because some
strings correspond to multiple OIDs. An example of such a string is
Bib-1 which may either be an attribute-set
or a diagnostic-set.
Applications using the YAZ database should include
yaz/oid_db.h.
A YAZ database handle is of type yaz_oid_db_t.
Actually that's a pointer. You need not think deal with that.
YAZ has a built-in database which can be considered "constant" for
most purposes.
We can get hold that by using function yaz_oid_std.
All functions with prefix yaz_string_to_oid
converts from class + string to OID. We have variants of this
operation due to different memory allocation strategies.
All functions with prefix
yaz_oid_to_string converts from OID to string
+ class.
Example 9.16. Create OID with YAZ DB
We can create an OID for the Bib-1 attribute set on the ODR stream odr with:
Odr_oid *bib1 =
yaz_string_to_oid_odr(yaz_oid_std(), CLASS_ATTSET, "Bib-1", odr);
This is more complex than using odr_getoidbystr.
You would only use yaz_string_to_oid_odr when the
string (here Bib-1) is supplied by a user or configuration.
All the object identifers in the standard OID database as returned
by yaz_oid_std can referenced directly in a
program as a constant OID.
Each constant OID is prefixed with yaz_oid_ -
followed by OID class (lowercase) - then by OID name (normalized and
lowercase).
See Appendix A, List of Object Identifiers for list of all object identifiers
built into YAZ.
These are declared in yaz/oid_std.h but are
included by yaz/oid_db.h as well.
Example 9.17. Use a built-in OID
We can allocate our own OID filled with the constant OID for Bib-1 with:
Odr_oid *bib1 = odr_oiddup(o, yaz_oid_attset_bib1);
The oident utility has been removed from YAZ version 3. This sub section only applies to YAZ version 2.
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_GENERAL
Use PROTO_Z3950 for Z39.50 Object Identifers,
PROTO_GENERAL for other types (such as
those associated with ILL).
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. Refer to the Registry of Z39.50 Object Identifiers for the whole list.
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.
Three utility functions are provided for translating OIDs'
symbolic names (e.g. Usmarc into OID structures
(int arrays) and strings containing the OID in dotted notation
(e.g. 1.2.840.10003.9.5.1). They are:
int *oid_name_to_oid(oid_class oclass, const char *name, int *oid);
char *oid_to_dotstring(const int *oid, char *oidbuf);
char *oid_name_to_dotstring(oid_class oclass, const char *name, char *oidbuf);
oid_name_to_oid()
translates the specified symbolic name,
interpreted as being of class oclass. (The
class must be specified as many symbolic names exist within
multiple classes - for example, Zthes is the
symbolic name of an attribute set, a schema and a tag-set.) The
sequence of integers representing the OID is written into the
area oid provided by the caller; it is the
caller's responsibility to ensure that this area is large enough
to contain the translated OID. As a convenience, the address of
the buffer (i.e. the value of oid) is
returned.
oid_to_dotstring()
Translates the int-array oid into a dotted
string which is written into the area oidbuf
supplied by the caller; it is the caller's responsibility to
ensure that this area is large enough. The address of the buffer
is returned.
oid_name_to_dotstring()
combines the previous two functions to derive a dotted string
representing the OID specified by oclass and
name, writing it into the buffer passed as
oidbuf and returning its address.
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.