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This page pertains to UD version 2.

CoNLL-U Format

Quick links: [Word segmentation] [Morphology] [Syntax] [Miscellaneous] [Extensions]

We use a revised version of the CoNLL-X format called CoNLL-U. Annotations are encoded in plain text files (UTF-8, normalized to NFC, using only the LF character as line break, including an LF character at the end of file) with three types of lines:

  1. Word lines containing the annotation of a word/token/node in 10 fields separated by single tab characters; see below.
  2. Blank lines marking sentence boundaries. The last line of each sentence is a blank line.
  3. Sentence-level comments starting with hash (#). Comment lines occur at the beginning of sentences, before word lines.

Sentences consist of one or more word lines, and word lines contain the following fields:

  1. ID: Word index, integer starting at 1 for each new sentence; may be a range for multiword tokens; may be a decimal number for empty nodes (decimal numbers can be lower than 1 but must be greater than 0).
  2. FORM: Word form or punctuation symbol.
  3. LEMMA: Lemma or stem of word form.
  4. UPOS: Universal part-of-speech tag.
  5. XPOS: Optional language-specific (or treebank-specific) part-of-speech / morphological tag; underscore if not available.
  6. FEATS: List of morphological features from the universal feature inventory or from a defined language-specific extension; underscore if not available.
  7. HEAD: Head of the current word, which is either a value of ID or zero (0).
  8. DEPREL: Universal dependency relation to the HEAD (root iff HEAD = 0) or a defined language-specific subtype of one.
  9. DEPS: Enhanced dependency graph in the form of a list of head-deprel pairs.
  10. MISC: Any other annotation.

The fields DEPS and MISC replace the obsolete fields PHEAD and PDEPREL of the CoNLL-X format. In addition, we have modified the usage of the ID, FORM, LEMMA, XPOS, FEATS and HEAD fields as explained below.

The fields must additionally meet the following constraints:

See the tools page for a list of tools that work with the CoNLL-U format. There is also a simple JavaScript-based CoNLL-U file viewer.

Words, Tokens and Empty Nodes

To accommodate the representation of both words and (multiword) tokens (see Tokenization and word segmentation), we adopt an extension of the original CoNLL-X token indexing scheme, where words are indexed with integers 1, 2, 3, …, while (multiword) tokens are indexed with integer ranges like 1-2 or 3-5. Lines representing such tokens are inserted before the first word in the range. These ranges must be nonempty and must not overlap. They have a FORM value – the string that occurs in the sentence – but have an underscore in all the remaining fields except MISC (because the token represents multiple words, each with its own lemma, part-of-speech tag, syntactic head, and so on). This is illustrated in the following annotation snippet, showing only the first three fields for the Spanish sentence vámonos al mar (let’s go to the sea):

1-2    vámonos   _
1      vamos     ir
2      nos       nosotros
3-4    al        _
3      a         a
4      el        el
5      mar       mar

We extract the word sequence by skipping all range IDs:

1      vamos     ir
2      nos       nosotros
3      a         a
4      el        el
5      mar       mar

We extract the raw token sequence by skipping all integer IDs that are included in a preceding range ID:

1-2    vámonos   _
3-4    al        _
5      mar       mar

Although multiword tokens normally cannot have any annotation in other columns than ID, FORM and MISC, there is one exception: The FEATS column may contain the feature Typo=Yes. For more information, see the page about Typos.

To accommodate the use of empty nodes for the analysis of ellipsis in the enhanced dependency representation, we adopt a further extension of the indexing scheme from v2. It is possible to insert one or more empty nodes indexed i.1, i.2, etc. immediately after a word with index i (where i = 0 for sentence-initial empty nodes). Note that the the numbers after the decimal point must form a sequence starting at 1, i.e. it is not allowed to skip i.1 and use i.2. In the unlikely case that there are ten or more empty nodes between two real tokens, i.10 comes after i.9, that is, the entire ID is not ordered numerically as a decimal number. Here is an example showing the use of an empty node in the analysis of the sentence Sue likes coffee and Bill tea:

1      Sue       Sue
2      likes     like
3      coffee    coffee
4      and       and
5      Bill      Bill
5.1    likes     like
6      tea       tea

Empty nodes must have non-empty ID and DEPS fields and empty fields (i.e. underscores) for HEAD and DEPREL, because they are only part of the enhanced dependency graph. All other fields may contain either underscores or values: for example, they can optionally have a word form and lemma as in the example above.

It is possible for an empty node to be positioned linearly between two syntactic words that are part of (the same) multiword token. It does not mean that the empty node is part of the multiword token, too. Multiword tokens are things that exist only in the surface sentence, while empty nodes are things that exist in the syntactic structure but not on the surface. Therefore empty nodes cannot be members of multiword tokens. Specifically, a multiword token range cannot be defined using an empty node ID (4-5.1 or 4.1-5 would be illegal).

If an empty node is positioned before the first word of a multiword token, it must also occur before the multiword token range line. Hence, the sequence 7 7.1 8-9 8 9 in the following example is valid, but 7 8-9 7.1 8 9 would be invalid (and so would be 7 8-9 8.1 8 9).

1      nosotros   nosotros
2      vamos      ir
3-4    al         _
3      a          a
4      el         el
5      mar        mar
6      y          y
7      vosotros   vosotros
7.1    vais       ir
8-9    al         _
8      a          a
9      el         el
10     parque     parque

Morphological Annotation

The UPOS field contains a part-of-speech tag from the universal POS tag set, while the XPOS optionally contains a language-specific (or even treebank-specific) part-of-speech / morphological tag, normally from a traditional, more fine-grained tagset. If the XPOS field is used, the README file of the treebank should define a mapping from XPOS to UPOS values (which may be context-sensitive and refer to other fields as well). If no language-specific tags are available, the XPOS field should contain an underscore for all words.

The FEATS field contains a list of morphological features, with vertical bar (|) as list separator and with underscore to represent the empty list. All features should be represented as attribute-value pairs, with an equals sign (=) separating the attribute from the value. In addition, features should as far as possible be selected from the universal feature inventory and be sorted alphabetically by attribute names. It is possible to declare that a feature has two or more values for a given word: Case=Acc,Dat. In this case, the values are sorted alphabetically. In sorting, uppercase letters are considered identical to their lowercase counterparts. Feature names must have the form [A-Z][A-Za-z0-9]*(\[[a-z0-9]+\])? and feature values must have the form [A-Z0-9][A-Za-z0-9]*.

Here is an example, showing only the first five fields for the Swedish sentence Då var han elva år (Then he was eleven years old):

1    Då      då     ADV      AB                    _
2    var     vara   VERB     VB.PRET.ACT           Tense=Past|Voice=Act
3    han     han    PRON     PN.UTR.SIN.DEF.NOM    Case=Nom|Definite=Def|Gender=Com|Number=Sing
4    elva    elva   NUM      RG.NOM                Case=Nom|NumType=Card
5    år      år     NOUN     NN.NEU.PLU.IND.NOM    Case=Nom|Definite=Ind|Gender=Neut|Number=Plur
6    .       .      PUNCT    DL.MAD                _

Morphological annotation is only provided for words. Tokens that are not words have an underscore in the UPOS, XPOS and FEATS fields, with one exception: The FEATS column may contain the feature Typo=Yes. For more information, see the page about Typos.

Syntactic Annotation

The HEAD and DEPREL fields are used to encode a dependency tree over words. The DEPREL value should be a universal dependency relation or a language-specific subtype of such a relation (defined in the language-specific documentation). As in the case of morphology, syntactic annotation is only provided for words, and tokens that are not words have an underscore in both the HEAD and DEPREL fields.

The HEAD and DEPREL values define the basic dependencies which must be strictly a tree. However, in addition to these basic dependencies, treebanks may optionally provide an enhanced dependency representation that specifies additional dependency relations, for example, when dependencies propagate over coordinate structures. The enhanced dependency representation, which in general is a graph and not a tree, is specified in the DEPS field, using a list of head-relation pairs. We use colon (:) to separate the head and relation and (as usual) vertical bar (|) to separate list items and underscore for the empty list. The list is to be sorted by the index of the head: 4:nsubj|11:nsubj.

Note that the DEPS field should be a self-contained representation of the enhanced dependency graph, which means that dependencies that are shared between the basic and the enhanced dependency representations must be repeated in the DEPS field. Here is an example, showing the first nine fields for the English sentence They buy and sell books:

1    They     they    PRON    PRP    Case=Nom|Number=Plur               2    nsubj    2:nsubj|4:nsubj
2    buy      buy     VERB    VBP    Number=Plur|Person=3|Tense=Pres    0    root     0:root
3    and      and     CCONJ   CC     _                                  4    cc       4:cc
4    sell     sell    VERB    VBP    Number=Plur|Person=3|Tense=Pres    2    conj     0:root|2:conj
5    books    book    NOUN    NNS    Number=Plur                        2    obj      2:obj|4:obj
6    .        .       PUNCT   .      _                                  2    punct    2:punct

On the other hand, if a treebank does not provide any enhanced representation, it is not necessary to copy all basic trees to DEPS, and it should be avoided in released UD treebanks (the DEPS field should be left unspecified instead).

The dependency relations in DEPREL must have the form [a-z]+(:[a-z]+)?. Certain extensions of this basic format will be allowed in DEPS but not in DEPREL; see the guidelines for the enhanced representation for details.

Miscellaneous

The final MISC field is for storing any additional information that does not fit into any of the other fields, such as language-specific annotation, any information about other linguistic levels such as discourse, or projective heads and dependency relations (cf. the old PHEAD and PDEPREL fields of the CoNLL-X format). The exact format used in this field should be specified in the treebank-specific documentation, but it has to be formatted as a list that can be split on the vertical bar character (|). If this character is needed in a value within the list, it must be escaped in a way that does not involve the character itself (for example, preceding the character with a backslash will not work and the vertical bar will still be considered a list separator). If the MISC field is not used, it should contain an underscore.

Untokenized Text

To facilitate reconstruction of original (pre-tokenization) text, the information on original word segmentation should be kept if available. If it is not available, UD treebanks since release 2.0 must approximate it using detokenization heuristics (see also the sentence-level attribute text below).

Every token after which there was no space in the original text should contain SpaceAfter=No in its MISC field. Note that this feature applies to the token level, not to the word level. Syntactic words that are just part of surface tokens will be ignored during detokenization and thus do not need the feature. In the example below, the line indexed 3 does not contain the SpaceAfter feature even though there was no space between für and das in the underlying sentence. However, if there were no space between fürs and the following token, the 3-4 line would have SpaceAfter=No.

Note that columns 5 to 9 are collapsed in the following example.

# text = Er arbeitet fürs FBI (deutsch etwa: „Bundesamt für Ermittlung“).
# text_en = He works for the FBI (German approx: “Bundesamt für Ermittlung”).
1     Er           er           PRON    …   _
2     arbeitet     arbeiten     VERB    …   _
3-4   fürs         _            _       …   _
3     für          für          ADP     …   _
4     das          der          DET     …   _
5     FBI          FBI          PROPN   …   _
6     (            (            PUNCT   …   SpaceAfter=No
7     deutsch      deutsch      ADV     …   _
8     etwa         etwa         ADV     …   SpaceAfter=No
9     :            :            PUNCT   …   _
10    „            „            PUNCT   …   SpaceAfter=No
11    Bundesamt    Bundesamt    NOUN    …   _
12    für          für          ADP     …   _
13    Ermittlung   Ermittlung   NOUN    …   SpaceAfter=No
14    “            “            PUNCT   …   SpaceAfter=No
15    )            )            PUNCT   …   SpaceAfter=No
16    .            .            PUNCT   …   _

Other Miscellaneous Attributes

Besides SpaceAfter=No, there are some other token- or word-level attributes that may be useful in multiple treebanks. These are not required; but if this sort of information is available, it is desirable that it is encoded the same way in all treebanks.

For a more comprehensive documentation of MISC attributes that have been used in various UD treebanks, see here.

Sentence Boundaries and Comments

There must be exactly one blank line after every sentence, including the last sentence in the file. Empty sentences are not allowed.

Lines starting with the # character and preceding a sentence are considered as carrying comments or metadata relevant to the following sentence. These lines are an integral part of the format as they give the ability to embed metadata together with the sentences. Consequently, any tools compatible with the CoNLL-U format should carry these lines over into their output (unless specifically designed to process them in some way). Comment and metadata lines inside sentences (i.e., between the token lines) are disallowed.

The contents of the comments and metadata is basically unrestricted and will vary depending on the application, but from v2 on the following two comments are compulsory for every sentence (and there must be just one comment of each kind per sentence):

Example:

# sent_id = 1
# text = They buy and sell books.
1   They     they    PRON    PRP    Case=Nom|Number=Plur               2   nsubj   2:nsubj|4:nsubj   _
2   buy      buy     VERB    VBP    Number=Plur|Person=3|Tense=Pres    0   root    0:root            _
3   and      and     CCONJ   CC     _                                  4   cc      4:cc              _
4   sell     sell    VERB    VBP    Number=Plur|Person=3|Tense=Pres    2   conj    0:root|2:conj     _
5   books    book    NOUN    NNS    Number=Plur                        2   obj     2:obj|4:obj       SpaceAfter=No
6   .        .       PUNCT   .      _                                  2   punct   2:punct           _

# sent_id = 2
# text = I have no clue.
1   I       I       PRON    PRP   Case=Nom|Number=Sing|Person=1     2   nsubj   _   _
2   have    have    VERB    VBP   Number=Sing|Person=1|Tense=Pres   0   root    _   _
3   no      no      DET     DT    PronType=Neg                      4   det     _   _
4   clue    clue    NOUN    NN    Number=Sing                       2   obj     _   SpaceAfter=No
5   .       .       PUNCT   .     _                                 2   punct   _   _

# sent_id = panc0.s4
# text = तत् यथानुश्रूयते।
# translit = tat yathānuśrūyate.
# text_fr = Voilà ce qui nous est parvenu par la tradition orale.
# text_en = This is what is heard.
1     तत्	तद्	DET     _   Case=Nom|…|PronType=Dem   3   nsubj    _   Translit=tat|LTranslit=tad|Gloss=it
2-3   यथानुश्रूयते	_	_       _   _                         _   _        _   SpaceAfter=No
2     यथा	यथा	ADV     _   PronType=Rel              3   advmod   _   Translit=yathā|LTranslit=yathā|Gloss=how
3     अनुश्रूयते   अनु-श्रु	VERB    _   Mood=Ind|…|Voice=Pass     0   root     _   Translit=anuśrūyate|LTranslit=anu-śru|Gloss=it-is-heard
4     ।      	।	PUNCT   _   _                         3   punct    _   Translit=.|LTranslit=.|Gloss=.

Note that some sentence-level comments may pertain to multiple following sentences, not just the one they immediately precede. This is the case of document and paragraph boundaries (described in the next section) but it may also hold for other, user-defined comments that are not specified here. The CoNLL-U format does not formally distinguish such comments from comments that really pertain to just one sentence; nevertheless, the files will be more readable if comments pertaining to larger segments precede comments pertaining to smaller segments. In particular, there is a comment that is defined in the extension CoNLL-U Plus, global.columns, which must appear as the first line of a CoNLL-U Plus file; while this comment is not part of the basic CoNLL-U specification, it is recommended that processing tools keep it as the first line if it is present. In general, it is recommended that tools keep the order of the comments unless they are specifically designed to modify it.

Paragraph and Document Boundaries

In addition, we define sentence-level and token-level comments (attributes) that mark paragraph and document boundaries. This kind of information is optional and sometimes it is not available (original text is lost, sentences have been shuffled etc.) but if it is available, it should be encoded in a unified way. Document and paragraph boundaries can be useful for various applications, including but not limited to sentence segmentation.

Note that while document boundaries always occur between sentences, paragraph boundaries may under certain circumstances occur in the middle of a sentence (bulleted list items, verse etc.) Document and/or paragraph boundaries are encoded as follows:

Note that the annotation defined in this section is observed by the conllu_to_text.pl script from the tools repository.

Example:

# newdoc id = mf920901-001
# newpar id = mf920901-001-p1
# sent_id = mf920901-001-p1s1A
# text = Slovenská ústava: pro i proti
# text_en = Slovak constitution: pros and cons
1   Slovenská   slovenský   ADJ     AAFS1----1A---- Case=Nom|Degree=Pos|Gender=Fem|Number=Sing|Polarity=Pos 2 amod _ _
2   ústava      ústava      NOUN    NNFS1-----A---- Case=Nom|Gender=Fem|Number=Sing|Polarity=Pos 0 root _ SpaceAfter=No
3   :           :           PUNCT   Z:------------- _          2       punct   _       _
4   pro         pro         ADP     RR--4---------- Case=Acc   2       appos   _       LId=pro-1
5   i           i           CCONJ   J^------------- _          6       cc      _       LId=i-1
6   proti       proti       ADP     RR--3---------- Case=Dat   4       conj    _       LId=proti-1

Extensions

See here for CoNLL-U Plus, a general template for extensions of the basic CoNLL-U format.