Legacy Issue Number: 16768
The Date-Time specification has verb concepts defining temporal relations to states of affairs that occur once, but not to states of affairs that recur. This means that the Date-Time specification cannot support all the needs of business concepts systems that are based on typical business language. The problem has also led to some erroneous formulations within the specification itself.
The relations to time include tense, aspect, duration, relations to time intervals (throughout/within/for/at/before/after <time interval>) and relative temporal positioning (before/after). They are defined for only the subset of states of affairs called “occurrences” and so are not helpful to semantic communities and businesses that refer to states of affairs more generally.
A common conceptualization approach is to objectify states of affairs, making them the subjects of verb concepts represented by adverbs, adjuncts and other verbal clauses. That approach, which often refers to states of affairs as “events”:
does not limit states of affairs to being in the subset that the Date-Time submission calls “occurrences”, but uses objectification generally for any event, activity, situation or circumstance;
is seen in modern language processing systems and their lexicons;
is a mainstream approach in the field of computational linguistics;
is a recommended approach in text books on mapping language to logic.
Whether a situation can recur across time depends on how the situation is identified, which is a conceptualization decision chosen by a semantic community. A situation that is identified without regard to time (e.g., the situation of a given person’s being in a given location, identified by person and location) can recur. The same situation occurs twice if the same person is in the same location twice.
Most verb concepts do not have roles that range over time, so their instances are identified independently of time. E.g., each instance of the verb concept ‘person is in place’ is identified by a person and a place. These instances are not “occurrences” as defined by the Date-Time specification because they can obtain at multiple different times. The same person can be in the same place multiple times.
The problem is illustrated in the following examples:
1. Consider the situation of there being snow in Seattle and a statement that the situation has occurred in the past, is not occurring now, and will occur in the future. The Date-Time vocabulary cannot be used for the three temporal relations in that statement; it includes a means to express such temporal relations, but not for situations that recur. An earlier version of the Date-Time submission supported this capability.
2. Consider the same situation of there being snow in Seattle, and that the situation occurred throughout both 12/25/2008 and 11/25/2010. “Throughout” from the Date-Time vocabulary cannot be used to say so. The Date-Time vocabulary does not define “throughout” generally for states of affairs (which includes situations). An earlier draft of Date-Time supported this capability.
3. It may be required to relate the same situation to its different occurrences. Date-Time defines “occurrence”, but does not provide the relationship between a state of affairs, such as the situation of there being snow in Seattle, and its separate occurrences. The Date-Time specification needs a verb concept by which a state of affairs can be related to its (possibly multiple) occurrences across time: ‘state of affairs has occurrence’.
4. In describing aspect and tense, the Date-Time specification shows incorrect formulations for some cases, partly because it does not relate states of affairs generally to time. Several specified formulations include “the occurrence (that John writes a book)”. But “that John writes a book” is a state of affairs that can recur it does not qualify as an “occurrence”.
Also, some of the formulations should use nesting, but don’t. E.g., “John will have written a book”, which is misformulated in the Date-Time table on tenses and aspects, can be properly formulated using nesting: “the occurrence (that the state of affairs (that John writes a book) has occurred) will occur”.
If the Date-Time specification is finalized without resolving these concerns, semantic communities will have to create their own temporal concept systems (or find another standard) in order to relate states of affairs generally to time. Those concept systems could adopt basic time concepts from the Date-Time specification, but would also need concepts for relating time to events, activities, situations and circumstance - and would not find them in the Date-Time specification. This would be an unfortunate shortcoming of the Date-Time specification.
SBVR’s usual practice is to objectify states of affairs in order to make them subjects of verb concepts, and to nominalize propositions only when propositions themselves are the subjects of discourse. This enables a first-order logic interpretation when discourse is about states of affairs and not about propositions. The Date-Time specification must also support this practice. There is a notion indicated in the Date-Time specification that propositions can be nominalized in order to relate states of affairs indirectly to time. People who want to nominalize propositions can, of course, do so but they need to be aware that doing so requires a problematic, higher-order approach.
Regardless of anyone’s interest in nominalizing propositions, states of affairs are commonly objectified in business discourse (such as in business rules) and are referenced by common terms (such as “situation”, “event”, “circumstance” and “activity”). If the Date-Time specification is to be used for business discourse, it needs to provide for relating time to states of affairs generally.
A resolution should provide verb concepts for relating states of affairs to time. A survey of business rules acquired from “business rules practitioners” shows that the following verb concepts will meet common needs for relating states of affairs to time.
The following verb concepts should be provided:
state of affairs occurs throughout time interval
state of affairs occurs within time interval
synonymous form: state of affairs occurs during time interval
state of affairs occurs for time interval
state of affairs1 occurs before state of affairs2 occurs
synonymous form: state of affairs2 occurs after state of affairs1 occurs
state of affairs1 occurs while state of affairs2 occurs
state of affairs has occurrence
The compound verb phrases using “starts” and “ends” that are already defined for “occurrence” could be added for states of affairs, but they are less important because they can be constructed. E.g., “John starts to eat before Mary comes home” can be formulated “(that (that John eats) starts) occurs before (that Mary comes home)”.
Also following verb concepts should be provided in support of tense/aspect for states of affairs:
state of affairs occurred
synonymous form: state of affairs happened
state of affairs has occurred
synonymous form: state of affairs has happened
state of affairs is occurring
synonymous form: state of affairs is happening
state of affairs will occur
synonymous form: state of affairs will happen
The compound cases of tense/ aspect, such as “will have ” are covered using the verb concepts listed above with nesting. E.g., “John will have eaten” can be formulated as “that (that (John eats) has occurred) will occur”. If compound forms are to be defined within the Date-Time specification, they should be defined by nesting the others.
The wordings for the four tense/aspect verb concepts above differ from wordings of similar verb concepts in the Date-Time specification for occurrences. This is deliberate in order to capture the intent of past, present perfect, present continuous and future as they occur in natural language. For example, a phrase like “is in the past” might be seen as appropriate about an occurrence that has already happened (since the time of an occurrence is intrinsic in its being an occurrence). Timing need not be intrinsic in a state of affairs, so a state of affairs that has occurred and that will occur again would not be understood as “is in the past”. It has occurred and it will occur.
Also, the Date-Time specification rightly defines “occurrence” as a specialization of SBVR’s ‘state of affairs’ by the way that it uses SBVR’s definition of ‘state of affairs’ within its definition of ‘occurrence’. Therefore, ‘state of affairs’ should be clearly indicated as a more general concept of ‘occurrence’.
Reported: DTV 1.0b1 — Tue, 29 Nov 2011 05:00 GMT
Disposition: Resolved — DTV 1.0b2
Most of the concerns raised by this issue are addressed by the resolution of issue 18173. This resolution contains changes that update table 16.1 to match the latest Date-Time terminology.
The authors of this issue apparently did not appreciate that the Date-Time Vocabulary permits 'occurrences' of a 'situation kind' (formerly 'situation model') to recur using the 'occurrence exemplifies situation model' verb concept. This aspect of the issue requires no change.
The beta-1 Date-Time specification explicitly avoided the term 'state of affairs' to avoid possible confusion at the request of the SBVR-RTF. Upon further discussion with the SBVR-RTF, the resolution of 18173 makes 'situation kind' (formerly 'situation model') and 'occurrence' specializations of 'state of affairs'. This solution integrates the Date-Time Vocabulary with "base" SBVR, thus:
Enabling objectification in the form called for in this issue.
Distinguishing potential states of affairs from occurrences, and enabling verb concepts to be explicit about their semantics.
The authors of this issue proposed a set of verb concepts that relate 'state of affairs' to time. The original proposal overlooks the fact that SBVR's 'state of affairs' concept is ambiguous: in some uses, it refers to potential situations (which may recur), and in other uses, it refers to what DTV calls 'occurrences'. The time relationships of each of these two aspects of 'state of affairs' are clarified in the existing Date-Time Vocabulary 'occurs' verb concepts.
This issue argues that the formulation "the occurrence (that John writes a book)" is invalid because "John writes a book" is a state of affairs, not an occurrence. With the 18173 resolution that 'occurrence' is a kind of 'state of affairs', this argument is incorrect. A sentence is added to the text to explain the formulation.
The issue also argues that formulations such as "John will have written a book" should use nesting. The FTF-2 agrees, and has updated table 16.1 to use nesting.
While preparing this resolution, the DTF FTF-2 noticed some minor corrections required to table 16.1 to make it match the latest Date-Time Vocabulary. These corrections are made in the following revised text.
Updated: Fri, 6 Mar 2015 20:58 GMT
DTV — Relating time to states of affairs
- Key: DTV-21
- OMG Task Force: Date-Time (DTV) 1.0 FTF