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Correspondence Metadata Interchange Format (CMIF)

Stefan Dumont, Ingo Börner, Jonas Müller-Laackman, Dominik Leipold, Gerlinde Schneider

Objectives and principles

  1The Correspondence Metadata Interchange Format (CMIF) was developed for editors of digital and printed scholarly editions to provide the most important metadata about edited letters online and in a machine-readable form. This allows for research, linking and analysis of correspondence across projects and editions.

  2On the basis of CMIF, researchers are able to search for letters from or to specific persons, places or within specific timespans across separate edition projects, which makes new comprehensive searches possible. For example, it makes it easier to search for letters by senders or recipients who do not have their correspondence covered in an individual letter edition. It is also possible to search for letters from a certain period, if necessary in connection with a certain place of dispatch or reception. With the implementation of version 2 one should be able to mark the entities mentioned in the letter (persons, places, publications, events etc.). As a result, it will be possible for the first time to use large collections of letters to answer systematic research questions such as how the music business was organized in the 19th century or how a certain event was received by contemporaries.

  3The CMIF - as a dedicated exchange format - covers exclusively metadata and these only in a focused form. It does not include full text data, not least to avoid legal problems. For the same reason, it can be distributed under a free license. It cannot be seen as a replacement for a complete and detailed teiHeader, which is specifically defined and used for individual editorial projects. The CMIF file is provided as an addition to a scholarly edition and is independent from the technologies and formats used for a given digital edition. Therefore, for the provision of the CMIF data, it does not matter whether the digital edition itself is based on XML, a relational database, or a graph database. After all, CMIF can also be used to provide the metadata of edited letters within a printed edition.

  4CMIF is intended exclusively for the exchange of relevant metadata beyond project boundaries. It includes only those metadata that appear useful for cross-project research, cross-linking and analysis. Put simply, the idea behind CMIF is that information found in the index of letters, person, places etc. of printed scholarly editions of correspondence can be provided digitally and in machine-readable form.

  5The CMIF should enable fully automated exchange of data without needing human intervention. To ensure this, the format must be restrictive and clearly defined. Accordingly, when developing the format, the guiding principle was "Keep it simple". By concentrating on essential metadata, the effort to provide a CMIF file should also be kept as small as possible. In addition, an online tool, the CMIF Creator, and detailed documentation are available.


  6CMIF is based on the guidelines of the Text Encoding Initiative (TEI) and was developed within the TEI Correspondence Special Interest Group (SIG). The initiative for the format was started in 2014 in the workshop "Briefeditionen um 1800: Schnittstellen finden und vernetzen", which was organized by Anne Baillot and Markus Schnöpf at the Berlin-Brandenburg Academy of Sciences and Humanities. Shortly before, a task force of the TEI Correspondence SIG (namely Marcel Illetschko, Sabine Seifert and Peter Stadler) had started to develop a new concept for encoding correspondence metadata for the TEI guidelines - realized in the new element <correspDesc> (Correspondence Description). It is supposed to encode the most important communication-specific "header data" of a letter in TEI-XML in a standardized way, in particular sender, recipient, place of writing and date. The proposal for correspDesc was accepted by the TEI Council, revised and incorporated into the TEI guidelines in April 2015. (Stadler, Illetschko, and Seifert 2016; TEI Consortium 2019).

  7Already during the development of correspDesc, Peter Stadler outlined the idea of developing a format for the exchange of correspondence metadata across editions based on this new element. The element correspDesc should be used in a significantly reduced and restrictive way to ensure an automated exchange of data. A first draft of CMIF was developed following the workshop mentioned above. Since then, CMIF has been developed and maintained within the framework of the TEI Correspondence SIG. The schema definition using ODD and examples can be found in the GitHub repository of the SIG.

  8The TELOTA working group of the Berlin-Brandenburg Academy of Sciences and Humanities developed the web service correspSearch in order to "fill CMIF with life", i.e. to demonstrate the possible application scenarios. It aggregates CMIF files available online and offers the metadata for convenient research or automatic retrieval via an API. The web service currently aggregates (as of 1.10.2019) 110 CMIF files with metadata to almost 54,000 edited letters in 178 publications. (Dumont 2016)

  9The Correspondence Metadata Interchange Format was awarded the "Rahtz Prize for TEI Ingenuity 2018" together with the element correspDesc and the web service correspSearch.

10In the course of the workshop “Herausforderungen der Briefkodierung” (“Challenges of letter encoding”) at the Berlin-Brandenburg Academy of Sciences and Humanities in October 2018, version 2 of the CMIF was developed based on the initial considerations.

General encoding principles

11The formulated principle also has implications for a decision between two variants for encoding. With regard to CMIF, two possible encoding variants exist within the framework of the TEI guidelines:

12On the one hand, it is possible to create one (albeit reduced) teiHeader per letter and to use its capabilities (profileDesc, msDesc, keywords etc.) to cover all necessary information. For an index of letters which includes the most important metadata, several teiHeaders could then - to put it simply - be combined in the element teiCorpus. Meta information on the letter index itself could then be stored in the teiHeader of the teiCorpus element itself.

13On the other hand, it is possible to create one single TEI document and provide one correspDesc element per letter there. With this variant, meta information on the CMIF file is directly indicated in the document's teiHeader.

14For the first version of CMIF, the second variant was chosen because it posed hardly any problems as the element correspDesc (together with its child elements) was completely sufficient for the desired metadata. In CMIF v1, only the sender, the recipient, places of writing and receiving, date and the URL or number of the letter are specified. This is what the TEI element correspDesc was and is designed for. All other information - which is very manageable in terms of numbers - can easily be placed in the teiHeader.

15With the further development of CMIF to version 2, however, further metadata - such as persons mentioned in a letter - for which the correspDesc element is not intended per se can now be noted. In this context it was discussed again whether one should not use the entire teiHeader per letter. At first glance, this seems to be a clean solution, but one creates a large "overhead" of TEI-XML encoding, which one would like to avoid for the reasons already mentioned - "keep it simple". In addition, such a teiHeader would still be greatly reduced compared to the teiHeader in the digital edition itself, but would at the same time suggest completeness. In addition, with the second encoding variant - i.e. the exclusive use of correspDesc - the CMIF can be further developed to be downward compatible. All further considerations are now based on the premise that the previously chosen encoding variant, which is essentially based on the use of correspDesc, will be retained.

16Here the fundamental question follows to what extent the CMIF should be conform to the TEI guidelines. So far, no major problems occured with the use of the TEI, which was essentially limited to the element correspDesc. But now - as already discussed (Dumont 2015) - various further aspects have to be integrated in correspDesc, which initially do not have their original location there. For certain purposes, new attributes of their own would appear desirable, but they would only be valid in CMIF and not generally in the TEI guidelines. Taking into account the fact that the CMIF is rooted in the TEI community and the acceptance based on it, the working group decided to focus on TEI conformity in the further development of the format. According to the definitions of the TEI guidelines, this includes, on the one hand, that the CMIF is validated against TEI All and, on the other hand, that the TEI Abstract Model is implemented correctly. A possible solution must take this into account.

Information to be included

17Following these preliminary considerations, the question arises as to which information should be included in the CMIF in addition to the information already available in version 1. Hereof it is necessary to take the objectives of the format postulated at the beginning into account: CMIF should enable both, cross-project searches for letters and automated analysis of metadata, for example for network research. The CMIF should not, as already mentioned, contain the full range of metadata that is generated within a letter edition. The relevance of the respective information for CMIF must be evaluated regarding its necessity and usefulness in cross-project research or analysis. This is not always a clear-cut decision. Of course, any information can increase the research and analysis benefit of the data. However, previous experience has shown that a cross-project metadata format is more accepted and used if only absolutely necessary information has to be provided. On the other hand, the effort for the project to provide its own metadata is the greater, the more information has to be provided. An information-saturated, but complex metadata format may seem ideal, but will find far less usage, which in turn greatly diminishes its usefulness. Consequently, for pragmatic reasons, the format should be kept manageable and simple.

Information Contained in CMIF v1

18Until now, CMIF mainly contained the communication-specific metadata of an edited letter: Sender, recipient, place of writing and receiving as well as corresponding date information. In addition, number and/or the URL of the letter can be noted. In addition, a bibliographic reference of the scholarly edition is listed in the teiHeader.

19Apart from these letter- or edition-related details, the CMIF file also contains metadata about the CMIF file itself (publisher, editor, creation or modification date and URL of the file).

Information to be included in CMIF v2

Archives and Editions

20In CMIF v2, it should be possible to note information on the identity of the letter in order to unambiguously identify or disambiguate it. This can be an archival signature, or a unique ID of a letter that is only printed. Such information is important in order to research other editions of the same letter (or to recognize them as such). The correspSearch web service already provides examples for this from the currently aggregated CMIF files, but these are not yet recognizable as such. The information is also important for the analysis of metadata from CMIF files, to prevent letters from being redundantly counted.

21Thus, references to the underlying archival document as well as to other editions of the same letter should be able to be noted in CMIF v2. This is relevant as automated differentiation or linking of letters is not possible without high error rates since there are too many cases in which different letters share the same basic data (sender, recipient, location, date). The archival information would be sufficient for identification, but there are also numerous cases in which the original letter (or its draft or copy) is lost or in (unknown) private possession. In these cases no archival information can be provided and references must be made from one edition to the other.


22The labelling of uncertain information is an important part of humanities scholarship - also when working with edited letters. Considering the use of CMIF metadata for digital research methods, such as historical network research, it should be possible for this information to be noted in the CMIF for the concerned data.

23This includes the labelling of information that could not be derived from the letter itself, but was taken from other sources or originates the researcher’s conclusion. Primarily this concerns the "header data" of a letter, such as sender and recipient, place of writing and receipt as well as the corresponding date information. Here it has always been common practice to place the respective data in the letterhead in square brackets to indicate that this information was "deduced" and could not be obtained from the original source itself.

24Deduced Information that does not originate from other sources but from the investigations of the editor, can appear to have less or more certainty. For example, if the editor is not sure about a particular information, it is not only marked with square brackets, but also with a question mark. This makes it possible to offer the reader a suggestion without specifying it is definitely correct. This practice of marking uncertain assumptions is not only used for the header data of a letter, but also in the body of the letter, if mentioned persons or places cannot be identified unambiguously.

25In addition to these two practices to label uncertainty, there is another one that concerns the letter as a whole: the copy text (textual basis). In general, a letter should be edited on the original manuscript. In case the original is lost, this is obviously not possible. For this reason, the textual basis is always specified in letter editions. Besides the original handwriting, this can be a copy by the author (or their scribe), a copy by the recipient, a concept, a draft or a later print. In any case, the existing textual basis implicitly indicates the certainty by which it can be assumed that the letter has reached its intended recipient and with what content.

Entities mentioned

26The user of an edition of correspondence is inevitably very interested in which letters certain persons, places, etc. are mentioned This is why properly prepared indexes are an important component of letter editions. The information contained in these registers is therefore also of great interest to CMIF. Information about which entities are mentioned in which letters would greatly facilitate research across editions or even make possible in the first place. In addition to “traditional” entity types found in the indexes of scholarly editions, such as persons and places, other types of entities are becoming increasingly of interest in recent years. These include primarily publications, however, also events, objects and quotations are feasible. The prerequisite for this would be the existence of authority files that provide identifiers for these types of entities so that they can be addressed across projects.

Type of publication

27So far, mainly edited letters have been discussed. However, historical correspondence is provided on different editorial levels by scholarship. These can range from simple archival repertories to regesta to fully edited letters which include commentaries and facsimiles. Information about the form in which a letter is ‘recorded’ is less relevant for scholarly questions that can be answered using metadata, however,it would support research in a meaningful way by enabling the user to see whatto expect at the end - whether it is printed or available online. This information would be particularly useful for scholars who want to build a corpus. In addition, it can easily happen that a letter is recorded differently in different projects. If data sets from both projects are to be used in a research interface, it is useful to be able to estimate the rough degree of recording there.


28Yet, it has to be answered how the desired information can be accommodated considering the background of the basic encoding (see above) and in a TEI-compliant way. If one wants to stick with the chosen approach and place all information in the element correspDesc, only the attributes in correspDesc and the child element correspDesc/note remain. The other two child elements correspAction and correspContext are semantically and uniquely assigned to the communication process so that they cannot be used as carriers for the additional information, as described above.

29In addition to the attributes, the element note, containing an "annotation" according to the TEI definition, remains in place. Although the information to be coded might not be covered by the proper meaning of “annotation” , the broader field of meanings attributed to “annotation” in the academic field is indeed much larger. Note can thus also be understood as an annotation of the correspondence description (correspDesc), which includes the information mentioned above.

30Once note has been chosen as a container, the question remains to what extent the listed information can be accommodated. Especially with regard to the mentioned entities it seems obvious to use the relevant TEI elements, such as persName. A coding would then look like this:

<note type="mentioned">
<persName ref="">Johann Wolfgang von
<placeName ref="">Mainz</placeName>
<orgName ref="http://asa">Verlag XY</orgName>
<bibl sameAs="">Die Leiden des jungen
<term ref="">Kalanchoe
<date from="1793-04-14" to="1793-07-23">Belagerung von Mainz</date>
Example 1: Encoding mentioned entities with specific TEI elements

31With this encoding, however, the question quickly arises as to whether one should go along in a more general way with rs (referencing string), which is specified via a @type attribute. An example based on a person would look like this:

<rs type="person" ref=""> Johann Wolfgang von
Example 2: Encoding information with generalized <rs>

32One advantage of this type of encoding would be a better flexibility when using different entity types. These will become more differentiated in the future and new ones will be added. For example, objects mentioned in letters that have actually been handed down in museums and collections are conceivable.

33Based on this generic approach, the working group came up with the idea of whether it would be possible to encode the references based on the triple notation of the Semantic Web. The references are noted as simple statements according to the pattern "subject - predicate - object". A natural linguistic analogy of a triple would be: "Letter XY mentions Johann Wolfgang von Goethe". For the purpose of machine-readable identification, corresponding URIs are used for subject and object, which are best defined across projects, e.g. in the common standards file. The predicate is also defined as a machine-readable URI. Eventually, this vocabulary would be part of CMIF v2. To encode such triples with TEI elements, the element relation is provided in the TEI guidelines. The example could then look like this:

<note type="mentioned">
<relation active="" name="cmif:mentionsPerson" passive=""> Johann Wolfgang von
Example 3: Encoding information as triple with the help of <relation>

34The example 3 shows an accurate and convincing encoding in terms of content. An advantage would also be that not only the mentioned entities, but also other desired information could be coded, such as the URI of the archival letter manuscript.

35In the beginning, various attributes in the element correspDesc were discussed, but it became clear that it would be difficult to find suitable ones for archival information etc. To give an example, the @corresp attribute could be used for the archive URI. The definition would allow this without further ado, but it is also ambiguous for it does not make a clear statement about the content. Beyond that it is desired to accommodate not only the URI of the archival document, but also URIs of other editions of the letter. All URIs could be noted in @corresp, but they could only be distinguished by their own names, e.g. by calling them or registering them in a processing web service, such as correspSearch. As a result, this would mean that this information would no longer be contained in CMIF itself.

36The proposed encoding with relations would therefore have the great advantage of accommodating all desired information specifically. However, it also has one disadvantage: this encoding is much more complicate than the other encoding approaches. CMIF should be as simple as possible - both in terms of the information to be included as well as the sort of encoding. Even so, could this not be solved more easily? If one were to encode all the desired information as in example 3, it would become apparent that the @active attribute always has the same URI - namely that of the edited letter. But this is already clearly defined by the element correspDesc as a whole and its attribute @ref. One idea would be to use the TEI element ref instead of relation:

<ref type="cmif:mentionsPerson" target="">Johann Wolfgang von Goethe</ref>
Example 4: Encoding information without the “subject” part.

37This way, one would stick to the approach with the exception that the redundant "subject", i.e. the edited letter in the form of a URI, would be omitted. The CMIF would remain clear and easy for people to understand.

Vocabulary and URIs

38If the ref element is used generically for further information in CMIF v2, it can be specified by the @type attribute to provide the differentiation required for research and analysis. The attribute value consists of a URI from a common vocabulary proposed in Table 1.

URI[1] Description @target (object)
cmif:mentionsPerson Person mentioned in the letter URI of the person (VIAF, GND etc.)
cmif:mentionsPlace Place mentioned in the letter URI of the place (GeoNames)
cmif:mentionsOrg Institution mentioned in the letter URI of the institution
cmif:mentionsBibl Publication mentioned in the letter URI of the publication
cmif:mentionsObject Object mentioned in the letter URI of the object
cmif:mentionsEvent Event mentioned in the letter URI of the event
cmif:isEditionOf The letter is an edition of an archival document URI of the archival document (e.g. Kalliope-URI)
cmif:seeAlso Other data record (e.g. in another edition) for the same letter URI of the (other) edited letter or record
cmif:hasTextBase Edited letter hat as textbase CMIF-URI (see table 2)
cmif:isPublishedWith Edited letter is published only as record or with regest, transcription, commentary. CMIF-URI (see table 3)
Table 1: Vocabulary for relationships (predicates)

39As in CMIF v1, URIs must be used for the targets (in ref/@target) in order to ensure machine-readable identification of persons, locations, etc. This assumes that there are suitable URIs for persons, places, etc. at all, which, if possible, originate from an authority file. This is certainly problematic as being discussed in the article on authority files. However, there are also numerous cases in which entities do not have to be defined across projects. In these cases, edition-internal URIs that identify or address corresponding entities are also conceivable, even if little is known about the entity. However, web services, which process CMIF files (e.g. correspSearch), have to retrieve data (names, life dates etc.) in a standardized way via the URI. This is currently neither customary nor sufficiently defined, so that further development is necessary. Nevertheless, CMIF v2 should already provide this option.

40In addition to URIs from authority files, a specific vocabulary is required that converts technical terms of scholarly editions of correspondence into a machine-readable format.

URI Definition
cmif:noTextBase Conjectured from mentions in other letters, diaries etc.
cmif:draft Draft
cmif:manuscript Manuscript
cmif:copy Copy (unspecified)
cmif:copy-by-sender Transcript (initiated or written) by the sender
cmif:copy-by-addressee Transcript (initiated or written) by the addressee
cmif:copy-by-third Transcript (initiated or written) by a third person
cmif:print Letter only survived in printed form
Table 2: Definition of Text Basis Types
URI Definition
cmif:record Record (only metadata)
cmif:abstract Regest
cmif:transcription Transcription
cmif:comment Commentary
cmif:facsimile Digital facsimile
Table 3: Type of information about the letter, provided in the scholarly edition

41The encoding of a text base and the information, the edited letter is published with, would then look like this:

<ref type="cmif:hasTextBase" target="cmif:manuscript"/><ref type="cmif:isPublishedWith" target="cmif:abstract"/>
Example 5: Text basis and type of available information about the letter


42This proposal for version 2 of the Correspondence Metadata Interchange Format is based on the principle that it should remain a lightweight, restrictive format. The CMI format provides only the most relevant information for research and analysis in order to maintain and further promote broad acceptance and usage in the community. In this context, attention is also paid to ensure fundamental conformance with the TEI guidelines.

43As in CMIF v1, the correspDesc element remains at the core of the format and includes all additional metadata. The proposed solution, based on correspDesc/note/ref, uses Semantic Web concepts such as a simplified but basically TEI-compliant triple notation, the use of URIs, and a controlled vocabulary in the CMIF namespace. This will allow to capture other important metadata - such as archival identifiers, uncertainties, and letter content - in a highly operationalized form and to provide it in a lightweight interchange format.

44After evaluating and integrating the feedback from the scholarly community, the proposal for CMIF v2 will be finalized in spring 2020 and published with documentation, ODD files and examples in the GitHub repository of the TEI Correspondence SIG.


  • [1]

    Here, the namespace prefix "cmif" stands for a namespace yet to be defined.



Stefan Dumont, Ingo Börner, Jonas Müller-Laackman, Dominik Leipold, Gerlinde Schneider: Correspondence Metadata Interchange Format (CMIF). In: Encoding Correspondence. A Manual for Encoding Letters and Postcards in TEI-XML and DTABf. Edited by Stefan Dumont, Susanne Haaf, and Sabine Seifert. Berlin 2019–2020. URL: URN: urn:nbn:de:kobv:b4-20200110163712891-8511250-2Zotero

Editorial Note

In this article, the following obvious misprints were corrected on 22 April 2020: Minor typo fixed and accidentally untranslated sentence (note 1) translated into English. In all other respects the article is unchanged in content and statement.