CANTUS is a database of Latin ecclesiastical chant, the earliest written musical repertory of any significant size. The texts are almost all in Latin, and the majority of them are drawn from the Bible, very often from the book of Psalms. There are thousands of individual chants, and they came into existence over a long period, beginning in early Christian times and continuing until as late as the nineteenth century. Virtually all chants have clearly defined liturgical roles that associate them with either the Mass or the Office, a series of worship services that take place at intervals through the course of each day. For the vast majority of chants, the date of composition is unknown, as is the composer. However, owing to the use of chant in worship in medieval times and beyond, and because chant melodies are often incorporated into the sacred music of the Middle Ages and Renaissance, scholars are deeply interested in learning all they can about it.

A formidable challenge in the study of medieval chant is the very large number of surviving sources and their considerable contents. Each hand-copied manuscript, which regularly may contain thousands of chants, is unique and testifies to the tradition of a specific time and place. Although the liturgy in the various antiphoners, graduals and breviaries is often similar from one book to another, the ordering, selection, and placement of specific chants can differ substantially. Owing to the volume of material and variability in arrangement, there is clearly a need for tools to assist in research involving these sources.

It uses as models two older kinds of indices--those published in various facsimile editions of sources (for example, Paléographie musicale), and those presented by Dom René-Jean Hesbert in Corpus Antiphonalium Officii [hence CAO]. CANTUS indices provide a flexible electronic format for the data they contain, and act as a supplement to earlier printed indices; a CANTUS index of a particular source will normally be used by a scholar who possesses a microfilm, facsimile or digital images of that source.

In CANTUS, each chant contained in a particular source is represented by one record. The fields employed in a CANTUS record are as follows: marginalia (or other specific uses as detailed in the "about" files for selected sources), folio number, an indication of the sequence of chants on the page or folio side, liturgical occasion ("feast"), textual incipit (limited to 29 characters), mode, differentia, CAO concordances (letters representing the sources surveyed by Hesbert in CAO in which the chant appears), chant ID number and CantusIDNumber (a field where chants which do not appear in CAO are included in such a way that they can be extracted from the file and printed in a separate list), Office, genre, liturgical position, an identifying number for each liturgical occasion ("feastcode"), manuscript siglum (identification of the manuscript source which is useful when indices are combined for sorting), and several extra fields in which additional information may be stored. See the Description of Fields and Their Contents for more details about each field.

It should be remembered that the flexibility of a computerized index greatly facilitates access to the information it contains. For example, one can learn within seconds whether a source contains a particular chant, and if so, exactly what its role is. One can also quickly locate the series of chants for a certain liturgical occasion. In addition, lists of certain types of chant can easily be prepared, such as an inventory of all the antiphons assigned to the Magnificat of Vespers and the Benedictus of Lauds (those normally indicated with the rubric "in evangelio").

Creating a tonary for an entire source, that is, listing all the antiphons by mode and differentia, is a relatively simple task if there is a CANTUS index for it; antiphons assigned to a certain mode and differentia can be printed in alphabetical order, or in liturgical order, or both. In addition, if one wishes to examine the melodies provided for those responsory verses that are not sung to the standard tones, finding them is a matter of just a few key-strokes.

CANTUS also makes it easier for the scholar to draw on information contained in CAO. One can prepare a list of all of the chants included in a CANTUS file that are also found in one or another of the sources indexed by Hesbert. The advantages over print-based media are obvious.

CANTUS files may be examined online, or readers may download the files for use on their own computers. When viewing the files online through a web-browser, a monospaced font will ensure that the characters are aligned properly. The "download" option allows for the extraction of a single manuscript index from the CANTUS database. The downloadable files are transferred in ASCII text (.txt)--this standard data format can be imported by the user into any word-processing programme or database.

Several of the CANTUS indices are available in book form; each includes an introduction that describes the manuscript and certain features of the chants it contains.