=Paper=
{{Paper
|id=None
|storemode=property
|title=Exploiting Inference to Improve Temporal RDF Annotations and Queries for Machine Reading
|pdfUrl=https://ceur-ws.org/Vol-966/STIDS2012_T13_Schrag_InferenceInTemporalRDF.pdf
|volume=Vol-966
|dblpUrl=https://dblp.org/rec/conf/stids/Schrag12a
}}
==Exploiting Inference to Improve Temporal RDF Annotations and Queries for Machine Reading==
Exploiting inference to improve temporal RDF annotations and queries for machine reading Robert C. Schrag Digital Sandbox, Inc. McLean, VA USA bschrag@dsbox.com Abstract—We describe existing and anticipated future benefits inferable bounds between any two points and will detect of an end-to-end methodology for annotating formal RDF contradictory time point relation sets. statements representing temporal knowledge to be extracted A fluent is an object-level, domain statement (e.g., FluentA: from text, as well as for authoring and validating test and/or attendsSchool(Jansa LubljanaUniversity)) whose truth value is application queries to exercise that knowledge. Extraction is a function of time. It is taken to be true at time points where it driven by a target ontology of temporal and domain concepts holds and not to be true at time points where it does not hold. supporting an intelligence analyst’s timeline tool. Both the tool We reify a fluent in an observation—a meta-level statement and the methodology are supported at several points by an implemented temporal reasoning engine, in a way that we argue whose object is a fluent, whose subject is a time interval, and ultimately advances machine reading technology by increasing whose predicate is a holds property (e.g., both sophistication and quality expectations about temporal holdsThroughout(FluentA Interval1), when FluentA is observed annotations and extraction. over Interval1, corresponding to, say, September, 1980). The events of interest to us, which we call transition events, Index Terms—temporal knowledge representation and occur at individual time points and may cause one or more reasoning, extracting formal knowledge from text, machine fluents to change truth value. We represent events (like the reading, annotation interfaces and validation birth of Jansa) as objects with attribute properties like agent, patient, and location, and we relate events to time intervals with I. INTRODUCTION an occurs property (e.g., occursAt(BirthOfJansa Point2), where Machine reading—that is, automatic extraction of formal Point2 is associated with an interval corresponding to the date knowledge from natural language text—has been a September 17, 1958). As usual with the event calculus, such longstanding goal of artificial intelligence. Effective extraction events can initiate fluents (e.g., occursAt(BirthOfJansa Point2) into RDF has the potential to make targeted knowledge initiates FluentB: alive(Jansa Interval3), where Interval3 is accessible in the semantic web. We recently supported a large- begun by Point2) or terminate them (e.g., DeathOfJansa… ). scale evaluation of temporal knowledge extraction from text by The temporal reasoning engine implements appropriate axioms providing RDF/OWL ontology for target statements and a to perform fluent initiation and termination. corresponding reasoning engine for query answering. Along Note that an observer may report information about the the way, we discovered… temporal extent of a fluent without communicating anything • How inference could improve annotation—the manual about initiation or termination. E.g., if text says Abdul and extraction of formal temporal statements—and Hasan lived next door to each other in Beirut in 1999, we don’t question authoring for evaluation or for applications. know when Abdul or Hasan may have moved to or from • How, coupled with annotation and question authoring Beirut. When text says Abdul moved to Beirut in 1995 and processes, inference could ultimately drive more emigrated in 2007, we use the properties clippedBackward and sophisticated machine reading capabilities. clippedForward regarding the fluent residesInGPE-spec(Abdul BeirutLebanon) to indicate initiation and termination by II. TEMPORAL KNOWLEDGE REPRESENTATION AND anonymous (unrepresented) transition events, so that we can REASONING FOR TIMELINE DEVELOPMENT also initiate or terminate temporally under-constrained like- Our temporal logic is based loosely on the event calculus fluent observations (e.g. Abdul lived in Beirut during the [10], as follows. 1990s). A time interval is a convex collection of time points— The reasoning engine’s implementation, using intuitively, an unbroken segment of a time line. Time intervals AllegroGraph, Allegro Prolog, and Allegro Common Lisp from begin and end with time points, which may be constrained Franz, Inc., can answer any conjunctive query. While not yet relative to each other or relative to a calendar. The ontology heavily optimized, it is at least fast enough to support machine includes a rich set of relational properties over time points and reading system evaluation over newspaper articles where cross- intervals, and the reasoning engine will calculate tightest document entity co-reference is not required. The combined extraction and reasoning capability was IV. LESSONS LEARNED WITH IMPLEMENTATION PROPOSED conceived to support an intelligence analyst’s timeline tool in Here, we propose some further approach elements that we which a GUI would be populated with statements about entities expect to lead to high-quality temporal annotations, (e.g., persons) of interest extracted from text. Our evaluation including… of machine reading capabilities was based on queries similar to A. Interfaces and workflows deliberately designed to those we would have expected from such a tool’s API. It also support capture of all statements specified as supposed the analysts could formulate their own, arbitrary extraction targets (see section A) questions, such as Query 1: Find all persons who were born in B. Graphical time map display including fluents and Ljubljana in the 1950s and attended Ljubljana University in the events (see section B) 1980s, the titles that they held, the organizations in which they held these titles, and the maximal known time periods over • On-line inference to elucidate inter- which they attended and held these titles. relationships and potential contradictions • Visual feedback to let users help assure quality III. LESSONS LEARNED AND REALIZED IN IMPLEMENTATION themselves This indirect, query answering style of machine reading • Time map-based widgets supporting user evaluation makes it especially important that we perform knowledge entry effective quality control of formal queries in the context of the C. Technology adaptable to test or application question formal statements we expect to be extracted from answer- authoring (see section C) bearing documents. We thus developed the test query D. Quantitative temporal relation annotation evaluation validation approach illustrated in Figure 1. Considering Query (see section V.A). 1’s formalization (see Figure 10 in section IV.B), it’s worth A. Annotation workflows noting that we used the methodology illustrated here to debug a Fluents are simple statements that we can readily represent number of subtle errors occurring in our earlier (manual) in RDF. The example in Figure 2 focuses on the fluent about formulations. When each such formulation did not result in the one Janez Jansa attending Ljubljana University—only on the answers expected, we traced inference to identify a point of failure, corrected this, and then iterated until correct. fluent, not the full observation including temporal information (i.e., only that Jansa attends the school, not when). The Our machine reading technologists told us early on that technology needed to annotate such information is well they preferred macro-level relational interfaces that would understood and (excepting perhaps the last bullet about streamline away micro-level details of time points and modality) has been well enough exercised that we may intervals. We thus provide a language of flexible specification routinely expect good results. This includes multi-frame GUIs strings (spec strings) that expand to create time points, where a user can produce stand-off annotations by highlighting intervals, and relations inside our reasoning engine. We also text and by clicking in drop-down boxes select relations, provide ontology to associate the temporal aspects Completed, classes, and instances. In part because these tools have Ongoing, and Future with fluents (e.g., he used to live there vs. preceded reading for formal knowledge extraction, they may he is living there vs. he is going to live there) and with the not use our intended representation internally—i.e., they may reporting dates of given articles, to afford a relational interface for historical reasons internally use a representation (e.g., XML reasonably close in form to natural language sources. For the that is not RDF) tailored to linguistic phenomena rather than Completed or Future aspects, we also can capture quantitative associated with any formal ontology. lag or lead information (e.g., he lived there five years ago or he will move in five days from now). Diagnose KR&R issues. Compare answers. Formalize. Given NL… Document Query Answer(s) Manually author selected Formalize Execute Produce statements to support query. query to KR… expected inference. get results. Apply temporal reasoning engine. Figure 1. We validate test queries by making sure that natural language (NL) and formal knowledge representation (KR) versions of documents, queries, and answers agree, diagnosing and debugging as necessary. 1. Select relation. …Jansa graduated from 2. Specify argument identifiers, respecting Ljubljana University… co-reference. Source text 3. Select / highlight / designate corresponding text. Formalization 4. Capture any counter-factual modality info. attendsSchool(Janez_Jansa Ljubljana_University) Figure 2. The workflow to annotate a fluent 1. Select one of time interval or point. Reporting date 2. Capture any beginning date and backward Dec 28, 2007… clipping info. 3. Capture any ending date and forward …Jansa graduated from clipping info. Ljubljana University in 4. Capture any duration info. 1984… 5. If ending point is unconstrained w.r.t. reporting date: a. Capture reporting aspect. b. Capture any reporting lag info. 6. Capture any other relative temporal info available. Fluent clipped forward at ending point attendsSchool(Janez_Jansa Ljubljana_University) 1984 Entered info (user writes) [,1984-12-31] [1984-01-01,1984-12-31] Inferred info (user reads) Figure 3. The workflow to annotate a holds statement (a fluent observation) Capturing the temporal information associated with the • There is no duration information. (We don’t know given observation of a fluent in a holds statement requires how long Jansa was at school.) following a sequence of actions and decisions in a deliberately • The ending point is well before the reporting date, so designed workflow, as outlined in Figure 3. We have we skip to the next step. highlighted, by color- and typeface-coding, some temporal • There is no other relevant temporal information. elements in the source text, along with corresponding steps in • To indicate clipping, the graphic fills the time point the workflow and elements of the associated graphical symbol (making it solid). representation. Our reasoning engine expands the entered coarse date 1984 Addressing the workflow step by step, we see that: into earliest and latest possible calendar dates bounding the • There is no reason to believe Jansa attended school for observation’s ending point. It also infers an upper bound on its only one day (the time unit associated with a time beginning time point. “point” in our machine reading evaluation), so we As illustrated in Figure 4, we invoke a similar workflow for choose a time interval (and the predicate event occurrence. Because our representation for events is holdsThroughout) rather than a time point (and simpler than that for observations, this workflow has fewer holdsAt). Schrag [8] argues that holdsAt almost never steps. Our ontology treats birth as a fluent transition event—it is appropriate, and in future this step may be omitted. occurs at a given time point, and it causes a transition of the • We find no beginning date information. (In the vital status of the person born (from FuturePerson to Alive). absence of such information, there is no benefit to Our graphical representation here accordingly just depicts a asserting backward clipping.) single time point (not an interval). We can use basically the • We find (and have highlighted) a coarse-grained same workflow to capture a non-transition event (e.g., a legal ending date (1984). We indicate that our fluent is trial) that occurs over more than one time point. clipped forward, assuming that Jansa no longer attends the school after graduation. …Born on September 17, 1. Select event type. 1958 in Ljubljana, Jansa… 2. Specify argument identifiers, respecting co-reference. 3. Select / highlight / designate corresponding text. 4. Capture any hypothetical modality info. 5. Capture any date info. 6. If an event’s date is otherwise unconstrained w.r.t. reporting date: BirthEvent(Janez_Jansa, Ljubljana) a. Capture reporting aspect. b. Capture any reporting lag info. 1958-09-17 7. Capture any other relative temporal info available. Figure 4. Workflow to annotate a transition event BirthEvent(Janez_Jansa, Ljubljana) On demand: 1958-09-17 • Trace back from bounds to user- attendsSchool(Janez_Jansa Ljubljana_University) entered information. [0D,15Y3M12D] o Date of the birth event [1958-09-18,1984-12-31] 1984 • Display / hide entered or inferred bounds on… Automatically: o Beginning points, ending points • Display in order any time points that are o Durations ordered unambiguously. • Focus on a particular time • Display inferred bounds. window, location, person, … o Rules: Can’t attend school before being • Highlight time points that are alive; being born makes one alive. ordered / unordered w.r.t. to a • Highlight bounds contradictions. selected, reference time point. Figure 5. A time map with both a fluent and a transition event judgments about the information they enter. If any inferred B. Displaying integrated time maps bound seemed odd, a user could click on it to identify which of Figure 5 illustrates a time map including both the birth his/her own entered information (then highlighted in the event and the school attendance fluent from earlier figures. It display) might be responsible. The time map display tool also suggests functional requirements to be satisfied would automatically launch such an interaction when it automatically/by default and upon user demand. Note that we detected a contradiction among inputs. now have automatically displayed—from on-line temporal The time map displayed in Figure 6 includes all the inference—a lower bound on the fluent observation’s information from the source text that is necessary to answer beginning date: Jansa could not have attended school until after Query1. The last fluent observation (at bottom right, where he was born. (The “day” time point granularity used in our Jansa is prime minister) exercises workflow steps that earlier machine reading evaluation leads to some non-intuitive effects, time map elements don’t. We have no ending date for this like not being alive until the day after one is born. We can observation, but we do have present tense reference to Jansa as easily correct this using an interval constraint propagation the prime minister, so we appeal to the reporting aspect arithmetic including infinitesimals [6][7][8].) We’ve also Ongoing. From the source text he was elected prime minister indicated bounds on the fluent observation’s duration on November 9, 2004, we can bound the observation’s (calculated as ending date bounds interval minus starting date beginning point. bounds interval). Propagating effects like this can maximize visual feedback to users, expanding their basis for quality BirthEvent(Janez_Jansa, Ljubljana) 1958-09-17 attendsSchool(Janez_Jansa Ljubljana_University) [0D,9235D] [1958-09-18,1984-12-31] 1984 personHasTitleInOrganization(Janez_Jansa Defence_Minister Slovenia) 1990 1994 personHasTitleInOrganization(Janez_Jansa Defence_Minister Slovenia) ElectionEvent(Slovenia, Prime_Minister, 2000 2000 2004-11-09 Janez_Jansa) personHasTitleInOrganization(Janez_Jansa Prime_Minister Slovenia) [2004-11-09, 2007-12-28] 2007-12-28 Slovenia national election day 2004, per user-established relative temporal Reporting date, via reporting reference aspect Ongoing Figure 6. A time map with more statements extracted from the same article ElectionEvent(Slovenia, Widget: User selects: Prime_Minister, • Relation (from menu) , Janez_Jansa) • Subject , object (via mouse) 2004-11-09 ‘ ‘ ‘ ‘ ‘ personHasTitleInOrganization(Janez_Jansa Prime_Minister Slovenia) ‘ ‘ Figure 7. Using the GUI to establish relative temporal reference Our user also has entered the election event. An election is access to these effectively, so that our user is empowered not necessarily a fluent transition event, at least in that an without being overwhelmed. elected candidate does not always take office immediately. So, Figure 8 shows formal statements that would be created we rely on the user to establish relative temporal reference directly by the user’s actions (i.e., not also including those between the election event and the fluent observation’s created indirectly by inference) in entering the information beginning. See the depicted constraint, whose entry is reflected in our finished time map. We have highlighted illustrated in Figure 7. Establishing relative temporal reference fluents and some other key statements, each of which appears requires the selection of a pair of time points and/or intervals to near several related statements. Our time map represents be related and of an appropriate temporal relation between Jansa’s birth event in a non-standard way, repeated here in them. Here, we just need the time point at which the election different color type, beside the italicized, standard statements. occurs to be less than or equal to the time point at which Jansa We have not similarly formalized the event of Jansa’s election takes office. as PM, and Figure 8 includes just statements about that event’s While a few common relations may be all that most users point of occurrence. will ever need, we do have a lot of relations [8] that a user Clearly, we can do a lot of formal work for the user behind could in principle choose from. We should be able to provide the scenes. F_school: attendsSchool (Janez_Jansa Ljubljana_University) holdsThroughout(F_school I_school) clippedForward(F_school I_school) hasTimeIntervalSpecString(I_school [,1984]) hasPersonBorn(birth Janez_Jansa) occursAt(birth P_birth) hasTimePointSpecString(P_birth 1958-09-17) BirthEvent(Janez_Jansa, Ljubljana) hasPersonBorn(birth Janez_Jansa) hasBirthEventGPE-spec(birth GPEspec) hasCityTownOrVillage(GPEspec ljubljana_Ljubljana_Slovenia) hasNationState(GPEspec Slovenia) type(Defence_Minister MinisterTitle) F_PTIO_DM_1: personHasTitleInOrganization(Janez_Jansa Defence_Minister Slovenia) holdsThroughout(F_PTIO_DM_1 I_PTIO_DM_1) clippedBackward(F_PTIO_DM_1 I_PTIO_DM_1) clippedForward(F_PTIO_DM_1 I_PTIO_DM_1) hasTimeIntervalSpecString(I_PTIO_DM_1 [1990,1994]) F_PTIO_DM_2: personHasTitleInOrganization(Janez_Jansa Defence_Minister Slovenia) holdsThroughout(F_PTIO_DM_2 I_PTIO_DM_2) clippedBackward(F_PTIO_DM_2 I_PTIO_DM_2) clippedforward(F_PTIO_DM_2 I_PTIO_DM_2) hasTimeIntervalSpecString(I_PTIO_DM_2 [2000,2000]) F_PTIO_PM: personHasTitleInOrganization(Janez_Jansa Prime_Minister Slovenia) holdsThroughout(F_PTIO_PM I_PTIO_PM) clippedBackward(F_PTIO_PM I_PTIO_PM) hasBeginningTimePoint(I_PTIO_PM I_PTIO_PM_beginning) hasTimePointSpecString(Slovenia_2004_Election_Day 2004-11-09) timePointGreaterThanOrEqualTo(I_PTIO_PM_beginning Slovenia_2004_Election_Day) hasReportingAspect(I_PTIO_PM Ongoing) ref(annotation I_PTIO_PM) annotation(document annotation) hasReportingChronusSpecString(document 2007-12-28) Figure 8. Formal statements associated with the time map in Figure 6 Query 1: Find all persons who were born in BirthEvent(?person, Ljubljana) Ljubljana in the 1950s and attended Ljubljana University in the 1980s, the titles that they held, the organizations in which they held these titles, and the maximal known time periods over which they attended and held these titles. 1950-01-01 1959-12-31 attendsSchool(?person Ljubljana_University) ?attendanceIntervalSpec 1980-01-01 1989-12-31 personHasTitleInOrganization(?person ?title ?org) ?titleIntervalSpec Figure 9. The time map covering our Query1 • We are asking about only one answer (set of variable C. Adaptation to test or application question authoring values satisfying the query) at a time. The supporting We might reuse much of the same machinery in a question statements in our earlier time map include three authoring interface, in which a user can formalize a query, as separate sets of bindings for the variables ?title and illustrated for Query1 in Figure 9. This time map display is ?org. even less cluttered than the one for this query’s supporting We have introduced intervals to represent the 1950s and the statements, for a couple of reasons. 1980s, and we have selected time point/interval relationships • We are making general statements, rather than specific appropriate to the query’s conditions. These relationships are ones, so don’t use as many dates or long identifiers. associated with particular idioms used in our formalization in Rather, we use variables (here beginning with ?). Figure 10. hasPersonBorn(?birth ?person) hasBirthEventGPE-spec(?birth ?GPEspec) hasCityTownOrVillage(?GPEspec ljubljana_Ljubljana_Slovenia) hasTimeIntervalSpecString(?I_range_birth [1950-01-01,1959-12-31]) occursWithin(?birth ?I_range_birth) hasTimeIntervalSpecString(?I_range_school [1980-01-01,1989-12-31]) holdsWithin(?F_school ?I_range_school) maximallyHoldsThroughout(?F_school ?I_school) hasTimeIntervalSpecString(?I_school ?attendanceIntervalSpec) ?F_title: personHasTitleInOrganization(?person ?title ?org) maximallyHoldsThroughout(?F_title ?I_title) hasTimeIntervalSpecString(?I_title ?titleIntervalSpec) Figure 10. Formalization of the query in Figure 9’s time map, covering Query 1 Our query asks about the “maximal known time periods” Others have applied limited temporal reasoning in post- over which the fluents hold, and we associate (via a query processing of temporal annotations, to… authoring workflow step) an “interval spec” variable with each A. Compute the closure of qualitative pairwise time fluent’s observation interval. Per our formalization, this will be interval relations, as one step in assessing a machine bound, on successful query execution, to a string that describes reader’s precision and recall performance (see section lower and upper bounds on the observation interval’s A) beginning point, ending point, and duration. The formalization B. Ascertain the global coherence of captured qualitative uses the properties occursWithin (for born in the 1950s) and relations (see section B). holdsWithin (for attended school in the 1980s) to accommodate Our implementation can go further, as described below. the temporal relations selected for the query authoring time A. Quantitative temporal relation annotation evaluation map. We know to use maximallyHoldsThroughout (vice the less restrictive holdsThroughout) for the fluents’ observation Evaluating temporal annotations typically has been limited intervals because the query’s author has included (via the to (Allen’s [1]) qualitative relations (e.g., before, overlaps, invoked widget) associated spec string variables. contains), and quantitative information about dates and Thus, it appears that we might enable non-specialists to durations typically has been evaluated only locally—at the author effective test queries (or, in a transition/application level of temporal expressions (AKA “TIMEXs” [3]). The setting, domain queries), without requiring the intervention of a reasoning applied has been strictly interval-based, neglecting KR specialist. One angle on this proposed work might be to important quantitative information about dates and durations determine the extent to which readers who are not (temporal) widely available in text. This approach is taken by Setzer et al. knowledge representation specialists can perform such tasks [9], e.g. consistently—alternatively, to determine the amount of training Our temporal reasoning engine, which is point-based, (e.g., pages of documentation, number of successfully naturally accommodates arbitrary bounds on the metric completed test exercises) required to qualify an otherwise-non- durations that separate time points and uses global constraint specialist to perform the task well. That said, rather than propagation to calculate earliest and latest possible dates/times “dumb down” the task, to accommodate non-expert readers, we for any point (including the beginning and ending points of all propose to ratchet up annotator performance expectations—to temporal intervals), as well as tightest bounds on durations. achieve the highest-quality results possible so that we can drive This approach also usually affords sufficient global research regarding extraction of temporal knowledge by perspective for a robust recall statistic. Adapting the standard machines from text to new levels of sophistication. The approach for evaluating interval relations [11], we can discard machine reading researchers whose systems are under from our gold standard annotations any redundant relations evaluation quite reasonably ask, before they embark on a until we determine a set spanning globally calculated bounds. mission of technological advancement, “Is this task feasible for Then we can count members of this spanning set whose humans, with acceptable consistency?” We’d like to answer addition to a user’s candidate set results in tightening of bounds that question in the best way that we can. in the latter, to determine recall. Only when every member of a set of points is unrelated to V. RELATED WORK AND PROPOSED ADVANCES the calendar (i.e., we have only point ordering and interval Beyond test questions and answers, the entire machine duration information) do we lack calendar bounds supporting reading community would benefit from having a large volume meaningful recall assessment. Then, however, by choosing any of good temporal logic annotations available. Time is a key point in a connected set to serve as a reference (in place of the topic in language understanding, engendering much current calendar), we can apply the same approach as above. community interest. TimeML [4], which emphasizes XML It may reasonably be argued that at some threshold of annotation structures rather than RDF ontology and representational complexity the brute force transitive closure- relationships, has been used in the TempEval temporal and-spanning tree approach to computing recall and precision annotation activities (see, e.g., www.timeml.org/tempeval2/) of an extracted knowledge base (set of statements) must and advanced as an international standard [5]. We are become impractical. 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