20 Using the XML Schema Processor for C

Oracle XML Schema for C Features

XML Schema processor for C has the following features:

• Supports simple and complex types

• Built on XML parser for C

• Supports the W3C XML Schema Recommendation

Standards Conformance

The Schema Processor conforms to the following standards:

• W3C recommendation for Extensible Markup Language (XML) 1.0

• W3C recommendation for Document Object Model Level 1.0

• W3C recommendation for Namespaces in XML

• W3C recommendation for XML Schema

XML Schema Processor for C: Supplied Software

Table 20-1 lists the supplied files and directories for this release.

Table 20-2 lists the included libraries in directory lib.

Using Transparent Mode

An application starts with a call to XmlEvCreateSVCtx(). This call creates and returns an event context of type xmlctx, which must be passed on all subsequent calls to the streaming validator. The event context created must be terminated by a call to XmlEvDestroyCtx().

After creation of the event context, the application repeatedly advances validation to the next event by issuing calls to XmlEvNext(), which returns the type of the next event. Additional API interfaces allow the application to retrieve information relevant to the last event.

# include "xmlev.h"
...
xmlevctx *ppevtcx, *svevctx;
xmlctx *xctx
xsdctx *sctx;
 
if (!(xctx = XmlCreate(&xerr, (oratext *) "test")))
    printf("Failed to create XML context, error %u\n",
                        (unsigned) xerr);
...
if (!(sctx = XmlSchemaCreate(xctx, &xerr, NULL))) 
    printf("Failed to create schema context, error %u\n",
                        (unsigned) xerr);
 
...
If (xerr = XmlSchemaLoad(sctx, "my_schema.xsd", NULL))
    printf("Failed to load schema, error %u\n",
                        (unsigned) xerr);

if(!(ppevctx = XmlEvCreatePPCtx(xctx, &xerr, NULL)))
   printf("Failed to create EVENT context, error %u\n",
                        (unsigned) xerr);
 
if(xerr = XmlEvLoadPPDoc(xctx, ppevctx, "file", "test.xml", 0, NULL))
   printf("Failed to load Document, error %u\n",
                        (unsigned) xerr);
 
...
If(!(svevctx = XmlEvCreateSVCtx(xctx, sctx, ppevctx, &xerr)))
   printf("Failed to create SVcontext, error %u\n",
                        (unsigned) xerr);
...
for(;;)
{
   xmlevtype cur_event;
   cur_event = XmlEvNext(svevctx);
   switch(cur_event)
    {
        case XML_EVENT_FATAL_ERROR:
           printf("FATAL ERROR");
           /* error processing goes here */
           return;
        case XML_EVENT_ERROR:
           XmlEvGetError(svevctx, oratext *msg);
           printf("Validation Failed, Error %s\n", msg);
           break;
        case XML_EVENT_START_ELEMENT:
           printf("<%s>", XmlEvGetName(svevctx));
           break;
...
        case XML_EVENT_END_DOCUMENT:
           printf("END DOCUMENT");
           return;
    }
}
...
XmlEvDestroySVCtx(svevctx); 
XmlSchemaDestroy(sctx);
XmlEvDestroyCtx(ppevctx);
XmlDestroyCtx(xctx);

Using Opaque Mode

In opaque mode, the streaming validator reads the instance document to be validated as a sequence of events from the producer, but does not pass the events to the application (consumer). It returns XMLERR_OK on success and an error number on failure.

After the schema has been loaded and the XML Events context has been initialized, the application can validate the document in this mode with a call to XmlEvSchemaValidate(). The signature of this function will take a pointer to the events context. The declaration is as follows:

xmlerr XmlEvSchemaValidate(xmlctx *xctx, xsdctx *sctx, xmlevctx *evctx, 
       oratext **errmsg);
/* Returns (xmlerr), the error code */

# include "xmlev.h"
...
xmlevctx *ppevtcx;
xmlctx   *xctx;
xsdctx   *sctx;
oratext  **errmsg;
xmlerr   xerr;
 
if (!(xctx = XmlCreate(&xerr, (oratext *) "test"))
      printf("Failed to create XML context, error %u\n", (unsigned) xerr);
...
if (!(sctx = XmlSchemaCreate(xctx, &xerr, NULL))) 
      printf("Failed to create schema context, error %u\n", (unsigned) xerr);
 
...
if (xerr = XmlSchemaLoad(sctx, "my_schema.xsd", NULL))
    printf("Failed to load schema, error %u\n", (unsigned) xerr);
 
if(!(ppevctx = XmlEvCreatePPCtx(xctx, &xerr, NULL)))
     printf("Failed to create EVENT context, error %u\n", (unsigned) xerr);
 
if(xerr = XmlEvLoadPPDoc(xctx, ppevctx, "file", "test.xml", 0, NULL))
   printf("Failed to load Document, error %u\n", (unsigned) xerr);

if((xerr = XmlEvSchemaValidate(xctx, sctx, ppevctx, errmsg)))
{
  printf("Validation Failed, Error: %s\n", errmsg);
}
...
XmlSchemaDestroy(sctx);
XmlEvDestroyCtx(ppevctx);
XmlDestroyCtx(xctx);

Enhancement of the Existing XmlSchemaLoad() Function

XmlSchemaLoad() was enhanced in Oracle Database 11g Release 1 (11.1) to work with an existing DOM. Previously, this function took two fixed arguments and a set of variable properties. The first argument is the schema context; the second is the URL location of the schema document. A new property was added to the set of variable arguments to provide access to the schema DOM given a URL. The property schema_dom_callback is a callback function provided by the application. If supplied, the schema load function will use this callback to access the DOM for the main schema as well as any included, imported, or redefined schemas. The callback signature is as follows:

typedef  xmldocnode* (*xmlsch_dom_callback) (xmlctx *xctx, oratext *uri, 
         xmlerr *xerr);

This callback accepts a URI (the schema load function will pass in the URI of the document desired) and returns the document node. An example follows:

# include "xmlev.h"
...
xmlctx *xctx;
xsdctx *sctx;
xmldocnode *doc;
 
if (!(xctx = XmlCreate(&xerr, (oratext *) "test"))
    printf("Failed to create XML context, error %u\n", (unsigned) xerr);
...
if (!(sctx = XmlSchemaCreate(xctx, &xerr, NULL))) 
    printf("Failed to create schema context, error %u\n", (unsigned) xerr);
...
If (xerr = XmlSchemaLoad(sctx, schema_uri, "schema_dom_callback", func1,  NULL))
    printf("Failed to load schema, error %u\n", (unsigned) xerr);
...
XmlSchemaDestroy(sctx);
XmlDestroyCtx(xctx);

Validation Options

You can supply options to the validation process using XmlSchemaSetValidateOptions(). For example:

XmlSchemaSetValidateOptions(scctx, "ignore_id_constraint", (boolean)TRUE, NULL);

The options are:

• ignore_id_constraint (existing before Oracle Database 11g Release 1 (11.1))

• ignore_sch_location (existing before Oracle Database 11g Release 1 (11.1))

• ignore_par_val_rest (existing before Oracle Database 11g Release 1 (11.1))

• ignore_pattern_check: When this property is TRUE, the streaming validator ignores pattern-facet checks. The default is FALSE.

• no_events_for_defaults: When this property is TRUE, the streaming validator will not return events for default values added to the instance document. This option can be used in the transparent case only.

# include "xmlev.h"
...
xmlevctx *ppevtcx;
xmlctx   *xctx;
xsdctx   *sctx;
xmlerr   xerr;
oratext  **errmsg;
 
if (!(xctx = XmlCreate(&xerr, (oratext *) "test"))
    printf("Failed to create XML context, error %u\n", (unsigned) xerr);
...
if (!(sctx = XmlSchemaCreate(xctx, &xerr, NULL))) 
    printf("Failed to create schema context, error %u\n", (unsigned) xerr);
...
If (xerr = XmlSchemaLoad(sctx, "my_schema.xsd", NULL))
    printf("Failed to load schema, error %u\n", (unsigned) xerr);
if(!(ppevctx = XmlEvCreatePPCtx(xctx, &xerr, "file", "test.xml", NULL)))
   printf("Failed to create EVENT context, error %u\n", (unsigned) xerr);
 
if(xerr = XmlEvLoadPPDoc(xctx, ppevctx, "file", "test.xml", 0, NULL))
   printf("Failed to load Document, error %u\n", (unsigned) xerr);
 
XmlSchemaSetValidateOptions(sctx, "ignore_id_constraint", TRUE,
                                  "ignore_pattern_facet", TRUE, NULL);
if((xerr = XmlEvSchemaValidate(xctx,sctx, ppevctx, errmsg)))
{
  printf("Validation Failed, Error: %s\n", errmsg);
}
...
XmlSchemaDestroy(sctx);
XmlEvDestroyCtx(ppevctx);
XmlDestroyCtx(xctx);