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YAZ Toolkit: Implementing Z39.50 Protocol for Information Retrieval

Learn about YAZ toolkit's powerful features for building Z39.50 servers and clients, memory management, query processing, and more. Get started now!

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YAZ Toolkit: Implementing Z39.50 Protocol for Information Retrieval

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  1. The YAZ Toolkit • Sebastian Hammer • Index Data - Information Retrieval consultants

  2. Why Toolkits? • Z39.50 is a machine-to-machine protocol • Good for software • Not friendly for people • Toolkits give you a programming interface • They hide encoding, network layer, error handling • Leave you to concentrate on your application

  3. YAZ • Z39.50 toolkit for Unix, Windows, etc. • ANSI-C, Portable, compact, easy to use • Widely used - constant feedback • Unlimited use license • Optional commercial support available

  4. Implementing Z39.50 • Building a server • Testing using third party clients • Building your own client

  5. The Z39.50 Server • Low-level YAZ API. Full access to Z39.50 protocol • Generic front-end server • Z39.50 server application • Simple high-level API to your ”back-end” • Standard daemon under Unix - multithreaded NT Service

  6. Generic Front-end Server API • #include <backend.h> • bend_initialize • bend_search • bend_fetch • bend_close • (bend_scan, etc.)

  7. bend_initialize • Verify authentication • Initialize instance of database back-end • Create session handle for private use • Return association accept/reject

  8. bend_close • Close database back-end instance (if relevant) • Release memory

  9. bend_search • Parameters • Database name • Result set name • Query • Result • Status • Number of hits

  10. bend_search bend_searchresult*bend_search( void *handle, bend_searchrequest *r);

  11. bend_searchrequest char *setname; int replace_set; int num_bases; char **basenames; Z_Query *query; ODR stream;

  12. Z_Query • Representation of Type-1 (RPN) query in C datatypes • Dangers: • Processing recursive data structure - ”easy”. • Interpreting the query honestly - HARD!

  13. RPN Processing Guidelines • Check for unsupported queries carefully • Attribute types/values • Operators • Operand types • etc. • Process attributes strictly • Provide good defaults for missing attributes

  14. Query Processing Thoughts • It is better to fail a query than to return incorrect results • Look at all attribute types/values. Reject unknown attributes • Set up clients so only good attributes are sent

  15. Memory Management Built-in memory pool manager • Allocation of protocol package elements • temporary memory for request processing • Memory recycled automatically

  16. bend_fetch • Parameters • Result set name • Offset • Result • Status • Record

  17. Retrieval Records • What record syntaxes do you need to support? • MARC = ISO2709 • SUTRS - Simple text format • GRS-1 - structured records • SGML/XML?

  18. The Z39.50 Client • Challenge: Integration with existing User interface / event paradigm • YAZ: C representation of Z39.50 protocol packages • Comstack API for exchanging protocol packages

  19. Z39.50 ASN.1 AttributesPlusTerm ::= SEQUENCE { attributeList SEQUENCE OF AttributeElement; term Term; };

  20. Z39.50 ASN.1 in C typedef struct Z_AttributesPlusTerm { int num_attributes; Z_AttributeElement **attributeList; Z_Term *term; } Z_AttributesPlusTerm;

  21. Comstack • Abstraction over transport service layer • Simplifies exchange of BER-encoded packages • Allows portability over transport stacks • You supply event-handling (”select”)

  22. ZAP - WWW/Z39.50 Gateway Environment • User interface - HTML forms • Results - based on templates containing bits of HTML • Quick prototyping • High performance under Apache webserver

  23. Other Options - scripting • IrTcl - Z39.50 package for TCL(TK) • High-level scripting environment • Incremental prototyping • Build platform-independent GUI clients or WWW gateways

  24. News? • Protocol encoders now ASN.1 compiler-generated • Easy to add or switch to new ASN.1 (eg. ILL) • Protocol package pretty-printing • Threadproof. Solid Windows port • Optional commercial support

  25. Where is it? www.indexdata.dk

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