Interlinear gloss

In linguistics and pedagogy, an interlinear gloss is a gloss placed between lines, such as between a line of original text and its translation into another language. When glossed, each line of the original text acquires one or more corresponding lines of transcription known as an interlinear text or interlinear glossed text an interlinear for short. Such glosses help the reader follow the relationship between the source text and its translation, and the structure of the original language. In its simplest form, an interlinear gloss is a literal, word-for-word translation of the source text.

History

Interlinear glosses have been used for a variety of purposes over a long period of time. One common usage has been to annotate bilingual textbooks for language education. This sort of interlinearization serves to help make the meaning of a source text explicit without attempting to formally model the structural characteristics of the source language.
Such annotations have occasionally been expressed not through interlinear layout, but rather through enumeration of words in the object and meta language. One such example is Wilhelm von Humboldt's annotation of Classical Nahuatl:
This "inline" style allows examples to be included within the flow of text, and for the word order of the target language to be written in an order which approximates the target language syntax. Even so, this approach requires the readers to "re-align" the correspondences between source and target forms.
More modern 19th- and 20th-century approaches took to glossing vertically, aligning the same sort of word-by-word content in such a way that the metalanguage terms were placed vertically below the source language terms. In this style, the given example might be rendered thus :
Here word ordering is determined by the syntax of the object language.
Finally, modern linguists have adopted the practice of using abbreviated grammatical category labels. A 2008 publication which repeats this example labels it as follows:
This approach is denser and also requires effort to read, but it is less reliant on the grammatical structure of the metalanguage for expressing the semantics of the target forms.
In computing, special text markers are provided in the Specials Unicode block to indicate the start and end of interlinear glosses.

Structure

Though there is no formal specification for the IGT format, the Leipzig Glossing Rules are a set of guidelines that aim to standardize the format as much as possible.
An interlinear text for linguistics will commonly consist of some or all of the following, usually in this order, from top to bottom:

The original orthography,
a conventional transliteration into the Latin alphabet,
a phonetic transcription,
a morphophonemic transliteration,
a word-by-word or morpheme-by-morpheme gloss, where morphemes within a word are separated by hyphens or other punctuation,

and finally

a free translation, which may be placed in a separate paragraph or on the facing page if the structures of the languages are too different for it to follow the text line by line.

As an example, the following Taiwanese Minnan clause has been transcribed with five lines of text:
Word-by-word alignment. According to the Leipzig Glossing Rules, it is standard to left-align the words in the object language with the corresponding words in the metalanguage; this alignment can be seen between lines and line.
Morpheme-by-morpheme correspondence. At the sub-word level, segmentable morphemes are separated by hyphens, both in the example and in the gloss. There should be the same number of hyphens in the example and in the gloss, as shown in the following example:
Grammatical category labels. In amuqʼ-da-č, the stem is translated into the corresponding English lexeme while the inflectional affixes and are inflectional affixes representing future tense and negation. These inflectional affixes are glossed as FUT and NEG; a list of standard abbreviations for grammatical categories that are widely used in linguistics can be found in the Leipzig Glossing Rules.
One-to-many correspondences. When a single object-language element corresponds to several metalanguage elements, they are separated by periods. E.g.,
Non-overt elements. if the morpheme-by-morpheme gloss contains an element that does not correspond to an overt element in the example, a standard strategy is to include an overt "ø" in the object-language text, which is separated by a hyphen like an overt element would be:
Reduplication is treated similarly to affixation but with a tilde that connects the copied element to the stem:

Punctuation

In interlinear morphological glosses, various forms of punctuation separate the glosses. Typically, the words are aligned with their glosses; within words, a hyphen is used when a boundary is marked in both the text and its gloss, a period when a boundary appears in only one. That is, there should be the same number of words separated with spaces in the text and its gloss, as well as the same number of hyphenated morphemes within a word and its gloss. This is the basic system, and can be applied universally. For example:
An underscore may be used instead of a period, as in go_out-, when a single word in the source language happens to correspond to a phrase in the glossing language, though a period would still be used for other situations, such as Greek oikíais house. 'to the houses'.
However, sometimes finer distinctions may be made. For example, clitics may be separated with a double hyphen rather than a hyphen. A French example:
Affixes which cause discontinuity may be set off by angle brackets, and reduplication with tildes, rather than with hyphens:
Morphemes which cannot be easily separated out, such as umlaut, may be marked with a backslash rather than a period:
A few other conventions which are sometimes seen are illustrated in the Leipzig Glossing Rules.

Interlinear gloss resources

Efforts have been undertaken to digitize IGT for hundreds of the world's languages.

Online Database of Interlinear Text

The Online Database of Interlinear Text is a database of over 200,000 instances of interlinear glosses for more than 1,500 languages extracted from scholarly linguistic research. The database was constructed in two phases: automatic construction followed by manual correction. The automatic construction stage itself was completed in three steps:

First, search engines were queried to retrieve scholarly documents that were likely to contain interlinear glosses. The queries comprised terms relevant to linguistic research such as grammatical morphemes.
Second, each line in an extracted document was tagged for whether it was a line belonging to an interlinear gloss or not using sequence-labeling methods from Machine Learning.
Third, each interlinear gloss instance was assigned a language name and an ISO 693-3 language ID. Language names and IDs were automatically assigned to interlinear glosses using Coreference Resolution models from Natural Language Processing, where the interlinear gloss instance was tagged with the language name that appears in the scholarly document the interlinear gloss instance was extracted from.

In the manual correction phase, the database creators manually corrected the boundaries of the interlinear gloss instances discovered by the sequence-labelling method in Step 2 of the automatic construction phase. The creators then verified the language names and language codes in a second and third pass over the data, respectively.

Range of interlinear gloss instances	Number of languages	Number of interlinear gloss instances	Percent of interlinear gloss instances
>10,000	3	36,691	19.39
1000-9999	37	97,158	51.34
100-999	122	40,260	21.27
10-99	326	12,822	6.78
1-9	838	2,313	1.22
Total	1,326	189,244	100

Automatic processing of interlinear gloss instances

Natural Language Processing models leveraging interlinear gloss resources, such as the Online Database of Interlinear Text, have been developed.

Automatic glossing

Natural Language Processing systems, for example, have been developed to automatically produce interlinear glosses.:
Given the morpheme segmented line and the free translation line, the task is to produce the middle glossed line comprising stem translations and the grammatical category labels corresponding to affixes. Sequence prediction models from Natural Language Processing have been used to perform this task. Two factors contribute to the difficulty of this task:

The translation is not necessarily in alignment with the morpheme segmented line.
Some words in the morpheme segmented line have multiple correspondences in the gloss.

Some constructed languages like Ithkuil and Lojban have automated tools that will always result in accurate glossing due to the regularized and logical nature of these languages. Here are examples of glosses of Ithkuil and Lojban respectively:

Automatic discovery of morphological structure from glosses

Researchers have used interlinear glosses to obtain the morphological paradigms of the object language. To automatically create morphological paradigms from interlinear glosses, researchers have created tables for every stem in the gloss and a slot for every grammatical category in the gloss. For instance, given the glossed sentence below:
There would be a paradigm for the stem pobeja with slots for PFV.PST.SG.FEM and PFV.PST.SG.MASC:

Slot	inflection
PFV.PST.SG.FEM	pobeja-la
PFV.PST.SG.MASC	?

The slot for PFV.PST.SG.FEM would be filled but the slot for PFV.PST.SG.MASC would be empty. A statistical machine learning model for morphological inflection can be used to fill in the missing entries.