Patent Grant
10296584
This application is the U.S. national phase of International Application No. PCT/GB2011/000102 filed 27 Jan. 2011 which designated the U.S. and claims priority to GB 10250157.4 filed 29 Jan. 2010, the entire contents of each of which are hereby incorporated by reference.
The present invention relates to a method of analysing textual phrases and in particular to a method of analysing the semantic content of textual phrases and determining semantic similarities between those phrases.
Information that is stored and organized within databases is conventionally referred to as structured information, whereas information that is described in natural language text is often referred to as unstructured, since many concepts can be expressed in multiple, and often imprecise ways, using natural language. There are a number of useful applications that are dependent upon the capability to process and analyse unstructured, natural language content, for example information retrieval (IR), document analysis and understanding, text summarization, machine translation, and question answering.
Natural Language Processing (NLP) tools are known, but methods and systems for Natural Language Understanding (NLU), question answering (QA) and advanced information retrieval (aIR) remain open topics in Computer Science. Given a passage of text, NLP tools can identify sentences, tag the parts of speech of words in that sentence, parse the sentence structure to identify grammatical components like noun and verb phrases, extract keywords, provide stemmed root words, resolve co-references, provide synonyms, perform named entity recognition (NER), and perform basic information retrieval like keyword-based search engines. However, advanced IR requires processing at the semantic level, which takes into consideration the meaning of phrases and sentences.
According to a first aspect of the present invention there is provided a method of determining a degree of semantic similarity between a first text phrase and a second text phrase, the method comprising the steps of: analysing the grammatical structure of the first text phrase and the second text phrase; processing the first text phrase to generate a first keyword set; processing the second text phrase to generate a second keyword set; and determining the semantic similarity between the first and second text phrases based on (i) the similarities between the grammatical structure of the first text phrase and the second text phrase; and (ii) the similarities between the first and second keyword sets.
If any idiomatic expressions are detected in step a), then one or more alternative expressions with a similar meaning to the or each idiomatic expressions may be identified. Step a) may comprise the parsing of the grammatical structure of each text phrase and inserting part of speech tags in accordance with the results of the parsing.
In steps b) and c) said first and second keyword sets may be generated by removing one or more stopwords from the respective text phrases. Steps b) and c) may also generate said first and second keyword sets by stemming the words comprising the respective text phrases.
The semantic similarity between the first and second text phrases may be used to determine the similarity of a first document to a second document. Furthermore, the decision to retrieve one or more documents may be made in accordance with the semantic similarity between the first and second text phrases.
Thus, if a requested phrase can be determined to be sufficiently similar to a key phrase which is associated with one or more documents, the or each document associated with the key phrase may be returned to the requester.
In an alternative application of the present invention, the semantic similarity between the first and second text phrases may be used to provide one or more answers in response to a received question.
Thus, in a support system, if a received question can be determined to be semantically similar to one or more questions that have been received previously then it is possible to respond automatically to the received question by returning answers that have previously been determined to be relevant to the received question.
According to a second aspect of the present invention there is provided an apparatus comprising a central processing unit, volatile data storage means and non volatile data storage means, the apparatus being configured to perform a method as described above.
According to a third aspect of the present invention there is provided a data carrier device comprising computer executable code for performing a method as described above.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
The present invention provides a method by which two text passages can be compared in order to determine the semantic similarity (or differences) between the text passages. The text passages may comprise a short phrase, a complete sentence, or multiple sentences. The semantic similarity may be expressed numerically using a passage semantic similarity measure (PSSM) which may take a value from 0 to 1, with 1 denoting that the passages are literally identical and 0 indicating that there is no semantic similarity between the two passages.
The two text passages which are to be compared are received by P1 at step S100 and are compared to determine if there is an exact match between them (this comparison is case insensitive). If the phrases are determined to be identical then at P2 (stage S102) a PSSM value of 1 is assigned and the method terminates. If the phrases are not identical then the method continues to P3 (stage S104) in which any contractions in the phrases are detected and expanded: for example the term “we'll” is converted to “we will”. A first flag is set to indicate that P3 has been performed and the method returns to P1 to determine whether the modified phrases are identical. For the case in which a contraction may have multiple expansions, for example “can't” can be expanded to both “can not” and “cannot”, then phrases which contain both (or each) of the multiple expansions are returned to P1 to determine if the phrases are identical. If the phrases are not identical then the method will continue to P4 (as the flag that was set after the completion of P3 prevents P3 from being repeated).
P4 (step S106) detects acronyms in the phrases and expands the acronyms such that the phrase includes all the valid terms that correspond to the acronym. For example, the term ‘FBI’ is expanded to ‘Federal Bureau of Investigation’. The method then returns to P1 such that the phrases can be compared to see if they are identical. A second flag is sent after the completion of P4 such that the process is not subsequently repeated. If the third instance of P1 does not detect that the phrases are the same then the method will continue to P5 (step S108). An exemplary operation of processes P1, P3 & P4 is shown below in Table 1.
P5 (stage S108) detects whether the phrases supplied by P4 comprise multiple sentences; if they don't then the method continues to process P7 (step S112). If a phrase does contain multiple sentences then in P6 (stage S110) a coreference resolution tool is applied and any detected pronouns are replaced by the original named entity. For example, if an input phrase comprised;
“HP Officejet 7410 is ideal for home and office use. It combines a scanner, fax machine, copier, and photo printer into one compact machine”
then it would be modified to the following;
“HP Officejet 7410 is ideal for home and office use. HP Officejet 7410 combines a scanner, fax machine, copier, and photo printer into one compact machine”
and this phrase is then sent to process P7 (step S112).
In process P7, each input text is scanned for known idiomatic expressions, for example by searching a known set of idiomatic expressions, such as, for example, idioms.thefreedictionary.com) and slang expressions, and additional alternate phrases are generated. Consider the following two phrases:
It is immediately apparent that these phrases are not literally identical and that both of these phrases have had any acronyms and/or contractions expanded. However, it would be clear to a speaker of English that the idiomatic expression “could not cut the mustard” is equivalent to the more formal phrase “could not meet the required standard”. When an idiomatic phrase is detected in P7, one or more alternate phrases can then be generated and used to supplement the original phrase. In the present case, Phrase B can be written as:
A knowledge module of idioms and slang expressions, with corresponding equivalent phrases, can be compiled from sources for idioms and slang expressions used in multiple countries. Supplemental knowledge modules may be used to add jargon and/or terminology that is specific to particular domains (e.g. medicine, different technical fields, law etc.).
Process P8 (S114) applies a known technique for named entity recognition (NER) to the text phrases. NER techniques identify common entities such as dates, phone numbers, location, such as countries, counties, cities, etc., personal names, events etc. During the execution of process P8 a knowledge module comprising popular and commonly used named entities may be accessed. This may be augmented by one or more supplemental knowledge modules (see below) which are specific to a particular technical or commercial domain or application. In process P9 (S116), the grammatical structure of the text phrases are analysed using a parsing tool and parts of speech (POS) tags are subsequently assigned to the words in the text phrases, including hierarchical groupings such as entire noun phrases, verb phrases, prepositional phrases, etc. The results of processes P8 & P9 enable the subsequent identification and independent comparisons of noun phrases, verb phrases, prepositional phrases, etc. that occur within the text phrases.
In process P10 (step S118), equivalent entity labels are applied to entities that were named during process P8 (e.g. people, places, events) so that alternate names are recognized as being equivalent. Original entity labels are preserved, and extra copies of text sentences are generated for subsequent augmented comparisons. For example, terms such as “Robert Wagoner” and “Bob Wagoner” or “White House” and “1600 Pennsylvania Avenue” are identified as being equivalent.
Referring to
The parts of speech (POS) tags that are generated by the output of the parser tool (see P9 above) can be used to ensure that different expressions of negation can be identified and marked. For example, when the parser tool is applied to Phrase B, as shown in Table 3 above, then the following results are obtained;
The tag ‘VP’ indicates a verb phrase, and the first verb phrase that follows the word ‘not’ will be the phrase that is negated by the word ‘not’. In the marked up text above, the term ‘meet required standard’ is shown in bold as this is the first verb phrase following the word ‘not’, and the verb phrase before the clause introduced by a subordinating conjunction, which is indicated by the ‘SBAR’ tag. Process P11 is also able to access the contents of an exception knowledge module (see below) so that negation exception terms such as “fail to” or “except” are also identified and marked, as they express negation in a different manner. Thus, one of the outcomes of P11 is that an expression such as
Process P12 (S122) recognizes and preserves important perception-based terms which relate to time, size, quantity, frequency, distance, temperature, sight, sound, smell, taste, touch, etc. such that they are not deleted by subsequent process P14 (S126), as the deletion of a single perception-based term could drastically change the meaning of phrases, and thus the outcome of any comparison results. For example, changing just a single frequency descriptor leads to significantly different meaning of the phrases “John frequently plays tennis” and “John seldom plays tennis”. A perception term knowledge module comprises a list of terms in each of the categories mentioned above, associated with terms for both a similar meaning and an opposite meaning. Hence, terms such as “often” would be associated has having a similar meaning as “frequently”, and the term “rarely” would be grouped as having the opposite meaning, together with terms such as “seldom”. As this knowledge module would not comprise a large number of terms and associations then it would be feasible to manually pre-specify the contents of the perception term knowledge module.
Process P13 (S124) detects modal qualifiers, for example will, shall, may, can, must, ought, etc. which are present in the text passages, as well as any usuality and probabilistic constraints which might alter the meaning of natural language phrases. In a similar manner to the perception term knowledge module, a modal term knowledge module may be constructed which comprises positive and negative association sets for the various modal terms. The relatively small number of terms that are required mean that construction of such a knowledge module is not an onerous task.
Processes P14-P17 perform a number of transformations on the text phrases. Process P14 (S126) detects and removes stopwords from the phrases. The resulting phrases are then stemmed in process P15 (S128), before the keywords are extracted from the phrases in process P16 (S130) and then those extracted keywords are expanded such that they are associated with relevant keywords (process P17, S132). It is preferred that the keyword extraction performed during process P16 is performed on the original text phrase, that is a copy of the text that is the input to process P1.
These operations are illustrated below in Table 4 with reference to the two text phrases that were discussed above in Tables 2 & 3:
In process P18 (S134), the selected keywords are grouped into N-grams for or further comparison of compound terms such as “special forces”. Matching synonyms from P17 are replaced in the output phrase generated by process P14 and n-gram analysis is then invoked for N=1, 2, 3. Where the text phrase comprises multiple alternate phrases (for example, B1 and B2 as shown in Table 4 above), the alternate phrase that has the most matches will be selected for propagation to the next stage.
Process P19 (S136) extends the semantic analysis to check for equivalent N-gram terms from an explanatory data source (for example Wikipedia). For the example shown above in Tables 2-4, the term “special operations” is found to be related to “special forces” during P19.
During process P19 (S136), n-grams from the unmatched portions of the phrase (e.g. for B2, the phrases “serve” and “special forces squad”) are further expanded to seek potential matches. This expansion process entails searching for the terms in an explanation/discussion source (for example Wikipedia). To reduce the possibility that the value of this process is reduced by excessive noise (effectively checking the N-gram terms against too many or irrelevant words) then the explanatory data source is limited, for example to the first few lines or sentences from the reference article or explanatory data source. The procedure starts with the largest (N=3) triplet “special forces squad”, and (when no matching explanation is found) repeats the process for N=2, and tries “special forces”. The explanation sentence is in the form X and Y are Z; hence it is logical to infer X (“special forces”) and Y (“special operations forces) are semantically related.
The result of P19 is a semantic key phrase set, which can then be used in P20 (S140) for the calculation of a numerical indicator of the similarity of the two phrases under consideration. After all the processing described above, the semantic key phrase sets derived from the example phrases under discussion are:
Thus, the two original text phrases that were lexically very different have been found to be semantically very similar. In process P20 (S140), a numerical indication of this semantic similarity, the Phrase Semantic Similarity Metric (PSSM) is determined. The PSSM is based on an aggregation of results which are generated by some of the previous processes which comprise a method according to the present invention.
where:
the set A comprises i={7, 8, 10, 11, 12, 13, 16, 18, 19}, where “i” corresponds to the process Pi, as described above with reference to
except for the case of
where N is the maximum value of the N-grams used in P18.
The PSSM value may simply be the value that is generated by equation [1]. In one embodiment of the present invention, the PSSM value may be truncated such that the PSSM value is in the interval [0, 1], where 1.0 is high similarity and 0.0 is low similarity.
Referring to the two phrases that have been used in the foregoing discussion of the present invention (see phrases 2-5), the PSSM value calculated from equation [1] is 1.1, which may be truncated to the maximum value of 1.0. indicating a high degree of semantic similarity between phrases A & B, despite the lexical differences between the two phrases.
Table 6 below shows two further phrases; it will be readily understood by an English speaker that Phrase C is less similar to Phrase A than Phrase B is, whilst Phrase D is semantically different from Phrase A.
Table 6 also shows the PSSM values for Phrases B, C & D when compared with Phrase A. As discussed above, Phrase B has a high PSSM, which indicates that there is a strong semantic similarity between the two phrases. Phrase C has a PSSM value of 0.57, indicating that there is some semantic similarity between Phrases A & C, but less of a similarity than there is between Phrases A & B. Phrase D has a low PSSM, indicating that there is a minimal semantic similarity between the two phrases. Thus, it can be seen that the PSSM value is an accurate indicator of the degree of semantic similarity that exists between two different test phrases.
Appendix A below provides a full description of the operation of a method according to the first embodiment of the present invention on these phrases, along with the determination of the PSSM values.
During the execution of a method according to the present invention, the output from each of the processes may be stored in memory for subsequent retrieval and/or processing. In the event that the apparatus that executes the method is severely constrained in terms of the memory and/or data storage that is available then it may be appropriate to discard some of the results obtained from intermediate processes. It will be understood that it would be preferred to retain the outputs from those processes that are used directly in the calculation of the PSSM value (that is processes 7, 8, 10, 11, 12, 13, 16, 18 & 19 [see above]).
The method discussed above describes a method in which two phrases are compared. For an application that required comparisons of multiple passages against each other, then a higher-level process could invoke the method of the present invention in repeated loops. For example, if it was required to compare 3 passages, the method described above could be invoked with passage pairs (P1, P2), (P1, P3), and (P2, P3).
It will be apparent to those skilled in the relevant technical field that most of the individual processes (P1 to P19) described above are known. Suitable examples of implementations of each of these processes, or further details of how such processes may be implemented, are given in Table 7 below. It will be understood that the list given in Table 7 is not exhaustive or prescriptive, and that other alternative methods may be used as an alternative or in addition.
Entities in Text”, M Dimitrov et al, Proceedings of the Fourth
Clinical Radiology Reports”, Huang Y., Lowe H. J. (2007) Journal of
using Natural Language Processing Techniques,” Yi J., Nasukawa T.,
natural language for a question answering system,” M. Thint, M.,
Stemming and Stopword Removal on Anti-spam Filtering Domain”
As will be understood by those who are skilled in the art, the various individual processes described above in Table 7 are all known in the prior art. It should be understood that it is the functionality of each process that is important to the operation of the method according to the present invention, as opposed to the particular algorithm or implementation of a process. Thus, alternative techniques to those examples given above in Table 7 may be employed as long as they provide the same or equivalent functionality. The preceding discussion of the present invention has referred to the invention being carried out on textual phrases that are in English. The inventors of the present invention believe that the present invention is also applicable to languages other than English. It will be understood that equivalents to the processes and techniques described in Table 7 above will be required for these other languages. If such techniques are not available in the prior art it would be a straightforward task for a person skilled in the art to derive such processes and techniques based on an understanding of the corresponding process for the English language and the linguistic and grammatical differences between English and the other language of interest.
A method according to the present invention will be implemented on a general purpose computing apparatus, such as a personal computer or a server computer which can be accessed by a client device or terminal.
The non volatile data storage means 230 comprises an operating system 232 and one or more application programmes 234. The operating system comprises the software that the computing apparatus requires to operate, communicate with other computers, receive input from users, display outputs and results to users, etc. Application programs 234 can be executed by the apparatus in order to provide additional functionality. Non volatile data storage means 230 further comprises computer code 236 which can be executed in order to perform a method according to the present invention, for example such as the one described above.
It will be understood that the computer code 236 may comprise a single integrated application, or a number of different modules that are accessed separately to execute a method according to the present invention. Each module may perform the functionality of one or more of the processes which comprise the present invention. As discussed above, a number of the processes (processes P3, P4, P7, P8, P10-P13 & P19) will need to access a knowledge module in order to be able to function. These knowledge modules are preferably separate (or separable) from either the single integrated application or the relevant software module such that it is possible for a knowledge module to be updated or replaced without effecting the logic of the software that accesses a knowledge module. The content of these knowledge modules may be downloaded from publically available sources or purchased from suppliers (see Table 7 above). It is also possible for a knowledge module to comprise a core module which may be supplemented by one or modules which are specific to a particular technical or knowledge domain.
It will be readily apparent to those skilled in the art that the apparatus 200 may be implemented in a number of different ways. For example, the text phrases may be input into the apparatus, for example by a user with a keyboard and mouse. Alternatively, the text phrases may be received via the network interface from one or more other computer apparatuses (not shown). In one particular embodiment, text phrases that are comprised within a body of user generated content, for example text within blog posts, messages or updates on social networking sites, etc. may be analysed by the apparatus, with text from the user generated content being copied to the non volatile data storage means for storage and subsequent analysis.
In a further embodiment, the computer code which can be executed in order to perform a method according to the present invention may be stored on and executed by the apparatus that is used to host a social networking site, online forum, user generated content service, blogging site, messaging service, user service site etc. A method according to the present invention may be used to identify questions which have been asked regarding the properties or expected operation of goods and/or services provided by a company or organisation or complaints which have been made regarding goods which are faulty or have operated in an unexpected manner such that customer service agents may make an appropriate intervention. Alternatively, if a question can be matched to other semantically similar questions then it may be possible to direct a user to one or more answers which have been identified (for example by user feedback and rating) as providing a useful solution to the question. Furthermore, a method according to the present invention can be used in a document retrieval system. A submitted query or question can be analysed and compared with a number of queries that are held within such a document retrieval system. If the submitted question has sufficient semantic similarity to one (or more) of the queries held within the document retrieval system then the documents which are pertinent to the query (or queries) are returned to the user who submitted the question. It will be understood by a person skilled in the art that a method according to the present invention is of significant utility across a range of applications and that the present invention is not to be limited to the uses discussed above.
The apparatus may comprise integrated display means and user input means for example a touch screen, for they may be separate, for example a conventional display screen and a keyboard and/or mouse. The non volatile data storage means may comprise one or more hard disc drives; in addition there may be provided removable non volatile data storage means, such as removable hard disc drives or optical media (for example re-writable or recordable DVDs). The network interface may be a local area network adaptor, with the LAN being connected to other LANs and wide area networks (WANs) to enable the apparatus to communicate with and exchange data with other computers. Alternatively, the network interface may be a DSL modem, or similar, that provides a connection to a WAN, such as the internet or an intranet, which enables communications with further networks.
It will be understood that the exact structure of the general purpose computing apparatus is not important as long as it is capable of executing the computer code which performs a method according to the present invention. Such computer code may be deployed to such a general purpose computing apparatus via download, for example via the internet, or on some physical media, for example, DVD, CD-ROM, USB memory stick, etc.
NOTE: As phrases differ in content and expression, some procedures may not produce new technical effect on its input data. For example, a phrase that does not use contractions can not be further processed by Process 3 (Expand contraction), and a “No-op” label is used to indicate a no-operation change.
| Number | Date | Country | Kind |
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| 10250157.4 | Jan 2010 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2011/000102 | 1/27/2011 | WO | 00 | 7/30/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/092465 | 8/4/2011 | WO | A |
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| Number | Date | Country | |
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| 20120303358 A1 | Nov 2012 | US |
