Information extraction

Information extraction (IE) is a type of information retrieval whose goal is to automatically extract structured information from unstructured machine-readable documents, generally human language texts by means of natural language processing (NLP).

Due to the difficulty of the problem, current approaches to IE focus on narrowly restricted domains. An example is the extraction from news wire reports of corporate mergers, such as denoted by the formal relation:

$MergerBetween(company_{1},company_{2},date)$,

from an online news sentence such as:

"Yesterday, New-York based Foo Inc. announced their acquisition of Bar Corp."

A broad goal of IE is to allow computation to be done on the previously unstructured data. A more specific goal is to allow logical reasoning to draw inferences based on the logical content of the input data. Structured data is semantically well-defined data from a chosen target domain, interpreted with respect to category and context.

History

Information extraction dates back to the late 1970s in the early days of NLP. An early commercial system from the mid 1980s was JASPER built for Reuters by the Carnegie Group with the aim of providing real-time financial news to financial traders.

Beginning in 1987, IE was spurred by a series of Message Understanding Conferences. MUC is a competition-based conference that focused on the following domains:

• MUC-1 (1987), MUC-2 (1989): Naval operations messages.
• MUC-3 (1991), MUC-4 (1992): Terrorism in Latin American countries.
• MUC-5 (1993): Joint ventures and microelectronics domain.
• MUC-6 (1995): News articles on management changes.
• MUC-7 (1998): Satellite launch reports.

Considerable support came from DARPA, the US defense agency, who wished to automate mundane tasks performed by government analysts, such as scanning newspapers for possible links to terrorism.

Present significance

The present significance of IE pertains to the growing amount of information available in unstructured form. Tim Berners-Lee, inventor of the world wide web, refers to the existing Internet as a document web and advocates that more of the content be made available as a data web. Until this transpires, the web largely consists of unstructured documents lacking semantic metadata. Knowledge contained within these documents can be made more accessible for machine processing by means of transformation into relational form, or by marking-up with XML tags. An intelligent agent monitoring a news data feed requires IE to transform unstructured data into something that can be reasoned with. A typical application of IE is to scan a set of documents written in a natural language and populate a database with the information extracted.

IE tasks and subtasks

Applying information extraction on text, is linked to the problem of text simplification in order to create a structured view of the information present in free text. The overall goal being to create a more easily machine-readable text to process the sentences. Typical subtasks of IE include:

• Named entity extraction which could include:
  • Named Entity Detection: detection (or discovery) of classes (or category) of entities such as "person", "location", "event" without having any existing knowledge about the entity instance. For example, saying that in the sentence "M.Smith like fishing" saying that "M.Smith" is a person without knowing which M.Smith we are exactly referring.
  • Named Entity Recognition: recognition of known entity names (for people and organizations), place names, temporal expressions, and certain types of numerical expressions. In the previous example, it will be to say that the sentence refer to a specific "M.Smith" on which we have extra information from other sentence and/or existing knowledge. Typically this involve assigning a unique identifier to the extracted entity.
  • Coreference resolution: detection of coreference and anaphoric links between text entities. In IE tasks, this is typically restricted in finding links between previously-extracted named entities. For example, "International Business Machines" and "IBM" refer to the same real-world entity. If we take the two sentences "M.Smith like fishing. But he doesn't like biking", it would be to detect that "he" is referring to the previously detected person "M.Smith".
  • Relationship Extraction: identification of relations between entities, such as:
    • PERSON works for ORGANIZATION (extracted from the sentence "Bill works for IBM.")
    • PERSON located in LOCATION (extracted from the sentence "Bill is in France.")
• Semi-structured information extraction which may refer to any IE that tries to restore some kind information structure that has been lost through publication such as:
  • Table extraction: finding and extracting tables from documents.
  • Comments extraction : extracting comments from actual content of article in order to restore the link between author of each sentences
• Language and vocabulary analysis
  • Terminology extraction: finding the relevant terms for a given corpus

Note that the exact meaning of IE activities is not commonly accepted and that many approaches combine multiple sub-tasks of IE in order to achieve a wider goal.

Information extraction and the World Wide Web

IE has been the focus of the MUC conferences. The proliferation of the Web, however, intensified the need for developing IE systems that help people to cope with the enormous amount of data that is available online. Systems that perform IE from online text, should meet the requirements of low cost, flexibility in development and easy adaptation to new domains. MUC systems fail to meet those criteria. Moreover, linguistic analysis performed for unstructured text does not exploit the HTML/XML tags and layout format that are available in online text. As a result, less linguistically intensive approaches have been developed for IE on the Web using wrappers, which are sets of highly accurate rules that extract a particular page's content. Manually developing wrappers has proved to be a time-consuming task, requiring a high-level of expertise. Machine learning techniques, either supervised or unsupervised, have been used to induce such rules automatically.

Wrappers typically handle highly structured collections of web pages, such as product catalogues and telephone directories. They fail, however, when the text type is less structured, which is also common on the Web. Recent effort on adaptive information extraction motivates the development of IE systems that can handle different types of text, from well-structured to almost free text -where common wrappers fail- including mixed types. Such systems can exploit shallow natural language knowledge and thus can be also applied to less structured text.

Approaches

Three standard approaches are now widely accepted for IE:

• Hand-written regular expressions (perhaps stacked)
• Using classifiers
  • Generative: Naïve Bayes
  • Discriminative: Maxent models
• Sequence models
  • Hidden Markov Model
  • CMMs/MEMMs
  • Conditional random fields (CRF) are commonly used in conjunction with IE for tasks as varied as extracting information from research papers to extracting navigation instructions.
    Main article: Conditional random field

Numerous other approaches exist for IE including hybrid approaches that combine some of the standard approaches previously listed.

Free or Open Source Information Extraction Software or Services

• General Architecture for Text Engineering "General Architecture for Text Engineering", which is bundled with a free Information Extraction system
• OpenCalais Automated information extraction web service from Thomson Reuters (Free limited version)
• Machine Learning for Language Toolkit (Mallet) is a Java-based package for a variety of natural language processing tasks, including information extraction.
• Apache Tika provides information extraction framework to parse textual content and meta data for several document formats
• See also CRF implementations

See also

• Concept mining
• DARPA TIPSTER Program
• Semantic translation
• Faceted search
• Named entity recognition
• Web scraping
• Nutch

External links

• MUC
• ACE (LDC)
• ACE (NIST)
• Alias-I "competition" page A listing of academic toolkits and industrial toolkits for natural language information extraction.
• Gabor Melli's page on IE Detailed description of the information extraction task.
• CRF++: Yet Another CRF toolkit
• A Survey of Web Information Extraction Systems A comprehensive survey.
• An information extraction framework A framework to develop and compare information extractors.