XML Proxy to Access Z39.50/MARC Capable Systems

Transcription

1 XML Proxy to Access Z39.50/MARC Capable Systems JOAQUIM A. MARTINS, HÉLDER ZAGALO, DANIEL SANTOS, SÉRGIO POSTILHÃO IEETA / Dep. Electrónica e Telecomunicações University of Aveiro Campus Universitário de Santiago, Aveiro, Portugal Abstract: - The objective of this work is to build a gateway to allow a Z39.50 distributed search system to have a friendlier web based user interface. To achieve this, a conversion between MARC and XML is done, using the Dublin Core profile to do the translation. This is also the base work to create a Web Service middleware to support a more generic and modular digital library search system. Key-Words: - Z39.50 protocol, XML, MARC, gateway, proxy, digital library 1 Introduction This work started as an add on to the project Memory of Africa, funded by the Foundation Portugal Africa (FPA), that implements a web based virtual catalogue ( -africa.ua.pt) with information about the resources of the new African Countries of Portuguese Language (PALOP). In order to extend the system to look for data in other bibliographic systems, was designed a distributed search module using the Z39.50 protocol. This module was also integrated in a project with the Portuguese Assembly of Republic to implement a digital library [1] [2]. To have a friendlier user interface and to integrate this module into a Web Services middleware architecture that supports the referred digital library was added an extra layer to convert de Z39.50/MARC data into XML data. The aim of the Z39.50 protocol is to allow the interoperability of bibliographic systems so that they can exchange bibliographic information among distributed libraries. It is a client server type protocol that runs on the Internet application layer. In order to normalize the communication between bibliographic computer systems the NISO (The National Information Standards Organization) established a committee to design a protocol to recover information. The studies began based on analyses done in the 70 s by the Library of Congress (LC) [3]: experimental protocol as part of the LC Linked System Project; 1979 The NISO setup a committee to design an information recovery protocol; 1988 The Z39.50 protocol first version was launched; 1991 Two Z39.50 complementary standards were approved by ISO; the ISO Search and Retrieve Application Service Definition (SR) and the ISO Interlibrary Loan Application Service Definition (IIL) The Z39.50 second version was launched and appeared many implementations. It was done also the harmonization with the standards of the American National Standards Institute (ANSI) and began it s widely adoption by the interested international community; 1995 Appeared the ANSI/NISO Z39.50 third version, with small enhancements, and started the study for the fourth version; The ANSI/NISO Z39.50 protocol can be implemented in any platform, allowing the interoperability between different bibliographic computer systems, which may have any kind of operating system, data bases and search systems. In this way the Z39.50 hides these differences allowing the user to have a transparent interface with multiple information systems. There isn t the need to learn new commands and search techniques since the results are presented in the local system, using formats that the users are used to. When there is the need to connect with multiple on-line catalogues, local or remote, this is a clear advantage. 1

2 The NISO committee that designed the Z39.50 protocol first version was dismissed after the protocol approval, in In 1990, a group of enterprises that develop Z39.50 software created the Z39.50 Implementors Group (ZIG), to promote and enhance the standard. When there is a new draft, is the NISO responsibility to assure that the ANSI procedures for voting and all other requirements be followed and that the ANSI final standard will be available for use. Working with the ZIG to promote the continuous protocol development, the NISO designated, in 1988, as Maintenance Agency for the Z39.50, the Library of Congress Network Development and MARC Standards Office. 2 The Z39.50 Protocol Basics The Z39.50 protocol divides the recovering information process in two main components: the information selection with a given criteria and information recovery. It offers also a common language for both operations and interoperability is achieved through the standardization of the coding mechanisms and semantics. The coding mechanism defines the messages (PDUs - Protocol Data Units) formats between the client (origin ) and the server (target) using the language ASN.1 (Abstract Syntax Notation One). This language describes data structures allowing transparency by acting as an intermediary language hiding the implementation and presentation local details. Regarding the transmission of those structures, they are coded using the BER (Basic Encoding Rules), which assure that the data that flows in the network is correctly understood by all the systems. Besides the message coding, the Z39.50 architectural model has the concept of semantic content. The server shows an abstract vision of its data base, based on records, within a given semantic domain. This virtual representation has records representing the logical structure of the real data base. Associated with each virtual data base there are a set of access points used to do searches and a set of return points used when recovering the records. Let s see the various session steps: Initialization this is the first service and is used to negotiate the other services and options that will be available during the session. Search this service allows very specific searches, as opposed to other search systems in which the user as no control over the search and introduces only some search words without being able to specify the subject of the search. The Z39.50 protocol has a rich mechanism that allows the classification of the search terms in several areas, known as attributes. We can have attributes like title, author, etc, enabling more focused searches. Recover this service is used to control the syntax and form of presenting the records to the user. The forms are Brief and Full and the most used syntaxes are the MARC variants (UNIMARC, USMARC, UKMARC...) [5]. The MARC (MAchine Readable Code) records are made up of numeric and alphanumeric identifiers and their contents. Each identifier defines a field, like title, author, subject, etc. Figure 1 shows a sample of these records. Close this ends the session ocm OCoLC s2000 maua eng DLC DLC C#P pcc HF B3 B / BWNA Burrows, William E Programming business applications with Microsoft Visual Basic 6.0 /William E. Burrows, Joseph D. Langford Microsoft Visual Basic Boston : Irwin, McGraw-Hill, c xviii, 680 p. : col. ill. ; 28 cm.+ 1 computer optical disc (4 3/4 in.) System requirements for accompanying computer disc: IBM PC, or 100% compatible with a Pentium 90 MHz processor, 16 MB of RAM, 4x CD-ROM, Microsoft Windows 95 or higher, and Microsoft Internet Explorer 4.01 or higher Includes index System requirements: Pentium/90 MHz processor; 16 MB RAM; Microsoft Windows 95 or higher, Microsoft Internet Explorer 4.01 or higher Microsoft Visual Basic for Windows BASIC (Computer program language) Business Computer programs Langford, Joseph D E0 BWN Figure 1 Example of a MARC record 2

3 3 Implementation of MARC to XML translation This work was based on a JAVA component, the Z39Client.jar, which establishes and manages the communications with several Z39.50 servers and allows, through a simple interface, to search and to recover bibliographic records. This information is returned in a rather cryptic way, as can be seen in figure 1, so the next step was to add some glue around this component in order to process this information. The information arrives in records with the ISO 2709 format, which is some form of MARC coding. The built component, Marc.jar, decodes the ISO 2709 records and presents them as a set of fields, each one with its own identifier. The fields are transformed into XML (Extensible Markup Language), using the Dublin Core [4] profile as model and the DOM (Document Object Model) platform to do the implementation, through the API JAXP (Java API for XML Parsing ) from Sun Microsystems. The Dublin Core is a model used to catalogue electronic resources, namely bibliographic data. The translation between MARC records and the Dublin Core elements was done accordingly with table 1. Some of the fields were ignored since they don t have useful information to the user. For example, in the case of figure 1, only the fields with identifiers 100 to 700 were processed, excluding the field 596. The Dublin Core qualifiers (see table 1) weren t also taken into account. In fact, the module responsible for this action - MarcDom.java - analyses the records and extracts the pertinent information without losses or repetitions (figure 2). Has the components are built using JAVA the site implementation was done using a capable JSP (Java Server Page) web server. The one chosen was the Resin(tm) [6]. The JSP does the interface with the user, using HTML (Hypertext Markup Language) to collect the data to do the search and passes them to the JAVA component that does the integration - Z3950process.java - and is the interface with the above described components. The system is very versatile allowing doing searches by title, author, subject or all fields. The data is validated using a Javascript function. The search results are returned in XML and formatted with a stylesheet XSL (Extensible Stylesheet Language) for user presentation. Dublin Core Element Dublin Core Qualifier Title 245 MARC fields Title Alternative 130, 210, 240, 242, 246, Creator 730, , 110, 111, 700, 710, Subject LCSH 711, , 610, 611, 630, 650 Subject MeSH 600, 610, 611, 630, 650 Subject LCC 050 Subject DDC 082 Subject UDC 080 Description ,except 505, 506, 520, 530, 540, 546 Description TableofCont 505 Description Abstract 520 Contributor Publisher Date Date Created Issued 260$a$b 260$c$g 533$d 260$c 008/07-10 Type DCMI Type Leader06, Leader07 Vocabulary 655 Format IMT 856$q Extent 300$a 533$e Medium 340$a Identifier URI 856$u Source URI 786$o Language ISO /35-37, 041 RFC Relation IsVersionOf 775,786$n$t Relation IsVersionOf 775,786$o Relation URI Has Version 775$n$t Relation HasVersion 775$o Relation URI IsReplacedBy 785$n$t Relation IsReplacedBy 785$o Relation Replaces 780$n$t Relation Replaces 780$o Relation Requires 538 Relation IsPartOf 760,773$n$t 490,800,810,811,830 Relation IsPartOf 760,773$o Relation URI HasPart 774$n$t Relation HasPart 774$o Relation URI IsReferencedBy 510 3

4 Relation IsFormatOf 776$n$t Relation IsFormatOf 530 Relation IsFormatOf URI 776$o, 530$u Relation HasFormat 776$n$t, 530 Relation HasFormat URI 776$o, 530$u Coverage Spatial 522, 651, 255, 650$z, Coverage Spatial $c,044$c ISO Spatial Coverage TGN Temporal 513$b, 033$a Rights 506, 540 Table 1 - Marc to Dublin Core Crosswalk (Qualified) So using interface systems like the XML one presented here hides this complexity and makes them much more user oriented and friendly. Besides that this XML presentation layer can be also the base to transform a Z39.50 server into Web Services if done in the server side, or through a proxy using a client Z39.50 as is the case in this work. Taking this step in order to exchange XML based data is the key to an even greater interoperability and simplicity of use of these systems. This is inline with the more recent proposals from the Z39.50 community which is taking the XML into account [3] [5]. 4 Conclusion The development of tools supporting the Z39.50 protocol allows a greater level of interoperability among bibliographic systems enabling the emergence of virtual bibliographic systems and, ultimately, distributed digital libraries. However the cryptic nature of the MARC codification and its several variants make it difficult to use for the common user. Figure 2 XML representation of a MARC record 4

5 References: [1] Joaquim Sousa Pinto, Helder Troca Zagalo, Joaquim Arnaldo Martins, Rui José Pereira Costa, "Portuguese Parliamentary Records Digital Library", In Ahmed K. Elmagarmid, Willian J. McIver Jr, "The Ongoing March Toward Digital Government", Computer, Vol. 34, Nº 2, p. 38, IEEE Computer, February [2] Joaquim Sousa Pinto, Joaquim Arnaldo Martins, Hélder Troca Zagalo, Pedro Almeida, Portuguese Parliamentary Records Digital Library, ICEIS International Conference on Enterprise Information Systems, AAAI/IEEE, Setúbal, Portugal, 7-10 July, [3] Z39.50 Maintenance Agenc y Library of Congress. (current ; last update August 2002). [4] MARC to Dublin Core Crosswalk: - intro, (current Sept. 2002; last update Feb. 2001). [5] MARC Standards - Library of Congress. (current Sept. 2002; last update Sept. 2002). [6] Resin Web Server, Resin tm Core, from Caucho. (current Sept. 2002). 5