The New Digital Joseph Haydn Catalog of Works orders Haydn's complete output chronologically and systematically at once, according to the present state of research. It is to replace the current reference, Anthony van Hoboken's Catalog of 1957 to 1978. Substantial fields of research must be worked through before then, from the watermarks to the study of the sources. Its basis is a continuous electronic signature already in use: the HW number. It identifies a work unambiguously, irrespective of genre, scoring and transmission, and remains valid even when the judgement on a work changes. A subsidiary project in preparation, the Catalog of Catalogs, is working through the principal Catalogs surrounding Haydn's output and forms the pool from which the new arrangement proceeds. The Hoboken number is carried forward as a historical document. The Catalog is not conceived as a book but as a body of data — machine-readable, with persistent identifiers and open standards. The working horizon extends to 2030.

The list of works is the entrance to the Catalog and its point of departure. It currently holds 982 works under the signatures HW0001 to HW0982. Works up to HW0799 are regarded as securely by Haydn; those from HW0800 onward were admitted because a historical Catalog lists them under his name — whether they are his is for source research to establish. It is therefore not settled that every work on this list will appear in the new Catalog. For each work the list records what first makes a work identifiable: title, key, scoring, date of origin, where applicable the librettist — and the Hoboken number, where one exists. Where none exists the entry reads deest, as a statement and not as a gap. Below the level of the work every movement is recorded, with tempo marking, key and time signature; at present that is 2,794 movements across 940 works. For 42 works the movement data is still outstanding — in part because the work is lost, in part because the recording has yet to be done.

The incipit is the most important means of identifying a work, and often the only reliable one. Titles migrate, scorings are rewritten, attributions change; the opening succession of notes remains. The incipit Catalog records the opening of every movement of the complete output, movement by movement and each assigned to its HW number; key, time signature, tempo marking and the notes themselves are recorded. Entered and encoded so far are 2,396 incipits across 937 works. They exist not as images but as musical text: first in MusicXML, then converted to MEI, the scholarly standard for the digital representation of music. This makes them searchable. A succession of notes can be queried like a word, and a find in another collection tested against the Catalog without anyone having to lay the music side by side. Each file carries a header with signature, movement, key, time signature, tempo and source, so that it remains legible outside its folder. Where no incipit yet exists, the gap is stated openly.

A wide field of people stood around Joseph Haydn: singers, instrumentalists, copyists, librettists and publishers — in short a team, without which Haydn could not have done his work. Their names appear in accounts, contracts, cast lists, concert bills and on the manuscripts themselves — mostly scattered, often variously spelled, rarely catalogued. The project Joseph Haydn Personalia Digital records these people prosopographically for the years 1761 to 1809: person, place, function, relation. Every name is checked against the Gemeinsame Normdatei, the German integrated authority file; where no record exists, one is created. A name on a sheet of paper thereby becomes an identifier that can be linked to other holdings. Only then does it become visible who worked for whom, when and where — and with that, when and in whose circle a given manuscript came into being. Anyone wishing to date a manuscript needs the person who wrote it. The project is in preparation; it builds on holdings already digitised.

No Catalog of works begins from nothing. Before Hoboken's Catalog, today's reference work, stood the historical Catalogs — the authoritative witnesses, silent and largely disregarded. The Entwurf-Katalog, which Haydn had drawn up around 1765 and continued for decades, is the earliest survey of his output made under his own hand. The Haydn-Verzeichnis of 1805, written out by his copyist Johann Elßler, is the last to be made in his lifetime. To these are added the Catalogs of the Viennese collector Aloys Fuchs. They are recorded leaf by leaf, incipit by incipit, in the order of the original and with its spelling. Since none of them carries a continuous, logically traceable numbering, each has been given one. Their incipits too are being made machine-readable, note for note. With Edirom the encoded incipit will be legible directly against the digitised Catalog page and cross-referenced with every other Catalog. What arises from this is a Catalog of Catalogs — the competing orders set side by side rather than replaced.

On the time of its making, paper often tells more than the notes upon it. Haydn wrote on paper of various origin, and each kind carries its own watermark. Italian paper shows above all the three crescents, English paper the fleur-de-lis, paper made at Lockenhaus the stag. Where a sheet came from is no minor matter: paper was expensive, was bought in lots, and under the intensity of the princely musical establishment was used up within a foreseeable time. If a kind of paper can be dated, so can the manuscript written on it — and with it a chronological attribution may be supported or refuted. The holdings are therefore recorded systematically by watermark: motif, countermark, mould construction, chain and laid line spacing. The records are linked to the established watermark databases, so that a finding in Vienna becomes comparable with one in Budapest or London. The fleur-de-lis in the emblem of Haydn Research Vienna comes from this very paper — from the English sheet Haydn used in his late years.

By far the greater part of the Haydn transmission is not in Haydn's hand. His music was spread through copies, written by copyists — foremost among them Johann Elßler, who worked for him for decades and whose hand is to be found as late as the final Catalogs. Beside him stood further scribes of the Esterházy chapel and the Viennese copying workshops. A scribal hand can be identified — by the drawing of the noteheads, by clefs and rests, by custodes and title inscriptions. Once identified, it becomes a means of dating: it shows when and in whose circle a copy was made, and which sources depend upon which. Essential here is the distinction between the copy taken directly from the autograph and the further copy made only from another copy. That line has not so far been drawn consistently — yet it decides the value of a source. Every hand identified is entered as a person and linked to the manuscripts in which it is attested. In this way a map slowly forms of the routes by which Haydn's music reached Europe.

In the two projects Joseph Haydn Digital and Joseph Haydn Digital 2.0, well over 90 per cent of the surviving Haydn autographs were brought together and made digitally accessible; the list of works records them. In the course of that work something happened which alters the view of the remainder: partial autographs came to light that had until then appeared in no Catalog — without particular effort and without anyone having searched for them. When unrecorded material surfaces incidentally, that argues that deliberate searching will bring more to light. Haydn Research Vienna proceeds on the assumption that further autographs are still in circulation, undiscovered. To pursue them is the purpose of source research. The work consists of autopsy, description and recording: identification of the scribal hand, recording of the watermark, registration of annotations, stamps and traces of provenance. Anyone who suspects a manuscript connected with Joseph Haydn is invited to make contact — including where the attribution is uncertain.