The COMARC/B machine readable format for bibliographic description and data exchange within the COBISS system is based on the UNIMARC format for bibliographic data, which is an international standard developed till March 2003 by IFLA's Universal Bibliographic Control and International MARC Programme (UBCIM) based in Deutsche Bibliothek, Frankfurt am Main. The UBCIM Programme was closed in March 2003 and the National Library of Portugal (NLP) took care for the further development of the UNIMARC format.

Besides the UNIMARC format standard fields/subfields, the COMARC/B format for bibliographic data includes a number of specific characteristics of bibliographic records structure within the COBISS system.

Except the COMARC/B format there are two other formats being used within the COBISS system: COMARC/H for holdings data and COMARC/A for authorities data; both formats are presented in separate handbooks.

During the implementation of UNIMARC format in the COBISS system, the handbook Priručnik za UNIMARC (Serbo-Croatian adaptation of the UNIMARC Manual, 1987) was used first. The manual was translated and adapted in 1989 in the National and University Library, Zagreb, and in the same year it was translated into Slovenian (Priročnik za UNIMARC) in the National and University Library, Ljubljana.

Together with the development of new functions within the COBISS system, it was also necessary to update UNIMARC format with new fields and subfields what led to the development of COMARC/B format. The Guidelines for Serials were published first as a constituent part of the Yugoslav bibliographic-cataloguing database (the Project Documentation), Maribor, December 18, 1990.

In 1991 the preparation of COMARC/B format for monographs, dissertations and serials followed, and afterwards also a number of other updates.

In 1994 the decision was reached to incorporate guidelines for different types of materials into one single format for bibliographic data – COMARC/B. Permission was obtained from IFLA UBCIM Program for using parts of translation of UNIMARC Manual. Bibliographic Format (UBCIM Publications – New Series, Vol. 14, 1994), 2nd Edition, in preparing the manual for COMARC/B format.

The improvement of the manual COMARC/B Format for bibliographic data, which is going to include all necessary guidelines from the UNIMARC Manual and all specifications within the COBISS system, will take place progressively over a period of time.

Fields/subfields are completely transferred from the segments "Dissertations" into the integral structure of the publication COMARC/B; the segment "Serials" is going to be transferred progressively into the integral structure of the manual. Specifications of a single bibliographic level and a type of material are going to be explained at separate field/subfield, and also corresponding instructions from UNIMARC Manual will be incorporated. Up to now all fields from blocks 0XX, 1XX, 2XX, 3XX and 4XX are transferred, and only some fields from other blocks.

In further updates of the COMARC/B manual only fields/subfields will be included, which are used in COBISS systems.

Fields/subfields that are not contained in UNIMARC, but are present in COMARC are marked by an asterisk "*"; fields/subfields that have been cancelled are marked by two asterisks "**". Fields/subfields appearing to be equal in both UNIMARC and COMARC, but having essentially modified meaning in COMARC, are going to be additionally described.

Fields/subfields, codes and indicators, that are not in UNIMARC, but are present in COMARC are marked by an asterisk "*"; fields/subfields, codes and indicators that have been cancelled are marked by two asterisks "**".

COMARC/B format is adapted to the COBISS shared cataloguing system which is described in the COBISS3/Cataloguing manual.

For data entry in the COBISS shared cataloguing system input masks are implemented which include a selection of fields and subfields being used frequently while entering data on a particular bibliographic level. All other fields may be used only if they are provided in a sample directory of the particular input mask.

The following input masks are implemented: M – monographs, K – continuing resources, Z – collections, A – articles and other component parts and N – non-book material.

Fields are designated by a string containing three numerals, and subfields are designated by a letter or a numeral. The smallest information unit being recognised by the programme is a subfield (search, display), i.e. a subfield element in COMARC/H format for holdings data.

Some fields have the indicator values defined usually signifying a display mode. In some cases fields and subfields are repeatable.

The Appendix A contains the list of all fields and subfields now used within the COBISS shared cataloguing system.

Punctuation marks between fields and subfields should not be entered strictly because they are generated automatically. A survey of all punctuation marks according to ISBD principles is shown in the Appendix B.

The Appendix C contains search indexes which may be used within the COBISS shared cataloguing system.

Multi-part monographic resources are described in the Appendix D.

The table of most frequent mathematical and other special characters appearing within titles, their entry and resolution in field 200 and other fields is shown in the Appendix E.

All specifications concerning bibliographies within the COBISS system from March 1996 onwards are described in the Appendix F1–F.8.

The Appendix G contains a code list of the UDC numbers assigned to the uniform search within the COBISS shared cataloguing system (subfield 675c).

Relator codes with their definitions are shown in the Appendix H.

In the Appendix I instructions are presented for cataloguing of collections. The data entry mode in separate fields of collective records is described, and also examples for separate fields are added, i.e. for complete records.

There are two types of examples at separate fields. Examples not specially marked were taken from the UNIMARC Manual. Bibliographic Format. They are all prepared according to different cataloguing rules and in different languages. That is why they do not always correspond to our cataloguing practise. With an asterisk "**" Slovenian examples are marked and also the examples from other libraries that are included in the COBISS.net network. The latter examples are also marked with the COBISS.net designation.

Experts from different institutions have participated, and still are participating, with their suggestions in the development of COMARC/B format. That is why, we are grateful to them for their work. In this development phase, certain suggestions have not yet been acted on, and will be adopted in the future.

All current and future users of this manual are invited to submit their suggestions and, in this way contribute and further improve solutions that have already been developed.