c - Redland RDF 库 : why does parsing model from Turtle without base URI cause error?

Question

为什么下面的测试会产生错误？是否Redland即使所有实际 URI 都是绝对的，'s turtle 解析器也坚持使用基本 URI？ (Apache Jena 显然没有。)我如何才能更多地了解实际出了什么问题(即什么 API 调用会返回错误描述或类似信息)？

librdf_world *world = librdf_new_world();
librdf_world_open(world);

librdf_storage *storage = librdf_new_storage(world, "memory", NULL, NULL);
librdf_model   *model   = librdf_new_model(world, storage, NULL);

librdf_parser* parser = librdf_new_parser(world, NULL, "text/turtle", NULL);

librdf_uri *baseUri = NULL;

const char *turtle = "<http://example.com/SomeSubject> <http://example.com/SomePredicate> <http://example.com/SomeObject> .";

int error = librdf_parser_parse_string_into_model(parser, (const unsigned char *)turtle, baseUri, model);

Answer 1

需要基本 URI，因为 parser says so using RAPTOR_SYNTAX_NEED_BASE_URI flag .它甚至在查看 raptor_parser_parse_start() 中的内容之前就产生了错误.

如果您知道不需要真正的基本 URI，则可以提供一个虚拟 URI，例如 。 代替:

librdf_uri *baseUri = librdf_new_uri(world, (const unsigned char *)".");

为了启用更好的错误报告，您应该使用 librdf_world_set_logger() 注册一个记录器- 默认记录器只是吐到 stderr。从记录器函数返回非 0 表示您自己处理消息。示例:

#include <librdf.h>

int customlogger(void *user_data, librdf_log_message *message) {
  fputs("mad custom logger: ", stderr);
  fputs(message->message, stderr);
  fputs("\n", stderr);
  return 1;
}

int main() {

  librdf_world *world = librdf_new_world();
  librdf_world_set_logger(world, /*user_data=*/ 0, customlogger);
  librdf_world_open(world);

  librdf_storage *storage = librdf_new_storage(world, "memory", NULL, NULL);
  librdf_model   *model   = librdf_new_model(world, storage, NULL);

  librdf_parser* parser = librdf_new_parser(world, NULL, "text/turtle", NULL);

  librdf_uri *baseUri = NULL;

  const char *turtle = "<http://example.com/SomeSubject> <http://example.com/SomePredicate> <http://example.com/SomeObject> .";

  int error = librdf_parser_parse_string_into_model(parser, (const unsigned char *)turtle, baseUri, model);

}

运行它会导致

mad custom logger: Missing base URI for turtle parser

(对于真正的程序，添加一些清理等)