A Novel Analysis of 
Temporal Frame-Adverbials 
Magnus MERKEL 
Department of Computer and Information Science 
Link6ping University 
S-581 83 LINKOPING 
SWEDEN 
Telephone: +46 13282423 
Internet: MME@IDA.LIU.SE 
Abstract 
In this paper interpretation principles for simple and complex 
frame-adverbial expressions are presented. Central to these 
principles is a distinction between phases and periods together 
with the temporal hierarchy, where multiple scales of time and 
relations can be expressed. A system, CLOCKWISE, has been 
implemented which interprets Swedish temporal expressions 
according to the principles outlined in the paper. 
Introduction 
Temporal information is expressed and conveyed in a number of 
ways in natural language including tense, aspect and lexical 
items that carry temporal information, eg. temporal adverbs. 
Most researchers in this field approach temporal entities in 
language from the perspective of tense and aspect. But there is 
very little in the literature on other expressions that hold tem- 
poral information, such as temporal adverbs, certain preposi- 
tional phrases and noun phrases. In most papers the meaning 
of a temporal adverbial such as 'next year' is merely explained 
as the predicate 'next year' which specifies a point or interval of 
time from a reference time. In objective time-modelling sys- 
tems such as/Kahn & Gorry 1977/and/Bruce 1973/ temporal 
expressions were never analyzed in their linguistic form; in- 
stead they had to be typed in as stereotyped lists. The internal 
structure of temporal expressions must be investigated in order 
to construct grammars that can capture general features and be 
of use in computational applications. In the paper I will focus on 
temporal frame-adverbial phrases, that is, expressions that 
refer to a temporal period in which events are located (Cf 
/Bennet& Partee 1978/,/Hinrichs 1986/). I will not discuss the 
complex question of how tense, aspect and temporal adverbials 
interact (for an outline of the problems see/Ejerhed 1987D. 
TemPoral frame.adverbial phrases 
A large group of temporal expressions can be classified as 
frame-adverbial phrases. /Smith 1981/ categorizes temporal 
frame-adverbial phrases in the following way1: 
Deictic Clock-Calendar 2 Dependent 
- last week, yesterday - at midnight 
= now, this moment 
+ next week, tomorrow + at midnight 
- previously, before 
= the same time 
+ later, afterwards 
1 My use of + and - is the same as Smith's forward and backward 
arrows. 
2 In an earlier paper (Smith 1980) Smith calls this class flexible 
anchoring adverbials. 
This classification is based on the concept of anchoring, ie. a 
deictic is generally anchored to the time of speech (ST), a de- 
pendent is anchored to another given time in the context, and a 
clock calendar adverbial can anchor to either ST or to some 
other context-dependent time. Smith attributes a relational 
value to these expressions, -, = and +. These symbols stand in 
turn for the relational value anteriority (past), simultaneity 
(present) and posteriority (future). 
Frame-adverbials can syntactically occur as adverbs, noun 
phrases and prepositional phrases. They can be complex ex- 
pressions such as 
(1) On Monday next week at 6 pro. 
where temporal information is specified on several levels and 
we have a combination of deictic and clock calendar expreso 
sions, Complex expressions have a relatively loose syntax in 
that the time denoted in (1) can be expressed as (2) and (3) 
(2) Next week on Monday at 6 pm. 
(3) At 6 pm next week on Monday. 
The issues that need considering are the following: How is the 
semantic well-formedness of frame-adverbial phrases deter- 
mined and, if possible, what is needed to establish their tem- 
poral reference in terms of locations on the time axis. 
Periods and phases 
To account for the semantic well-formedness of flame-adver- 
bial phrases the 'time' denoted by the phrase can be thought of 
as an ordered set of specifications for conventional temporal 
concepts, such as YEAR, MONTH, DAY, HOUR, MINUTE, 
SECOND. The ordering of these temporal concepts may seem 
to fit well into a 'Chinese box metaphor' where each concept is ~ 
included in a concept on a higher level and in turn includes a 
concept on a lower level. A semantically well-formed temporal 
frame-adverbial would then be described as a phrase which 
forms a description of an unbroken chain of temporal concepts. 
This is put forward by/Hinriehs 1986/in his Scoreboard of 
reference points and cooccurence restriction in which the con- 
struction of a reference time from a flame-adverbial phrase is 
possible if there is a chain of specified temporal concepts in 
accordance with an ordered set of concepts. However, if we in- 
cluded WEEK in the above set of concepts we would get into 
trouble. Weeks are not included in months in the same way as 
months are included in years and a problem of where to fit in 
WEEK in the Chinese box order would occur. This is due to the 
fact that the western calendar system is based on three sepao 
rate descriptive traditions: the week, the Gregorian calendar 
and the clock/Levy 1980/. The Gregorian calendar holds year, 
month and day(of month) as its basic concepts, the week is a 
sequence of named days, and the clock system divides the day 
into hours and hours into seconds, etc. The week and 
Gregorian calendar share the concept of day and the clock 
426 
system split.~ the day into time segments. The reason that we 
can express a time by specifying different concepts of separate 
systems is that the systems share one or more concepts with 
each other, tlt is also reflected in the way we refer to the day 
period (in S ~vedish and English). A day can be referred to in 
two different ways, either by specifying the day of a certain 
week (DW) or by picking out a day of a certain month (DATE). 
In English the expression on Monday next week will describe 
the same day on the time axis as an expression describing the 
same day by specifying a year, a month and a day of month. In 
Swedish it is possible to specify a mfique day by the year- 
week-day path as the Swedish calendar has numbered weeks, 
giving us a year divided into 53 weeks 3. 
In our model we want to distinguish between periods and 
phases and ~;how the relations between them. 
A period P is a segment of time with a certain length, such as 
YEAR, MONTH, DAY, WEEK, HOUR, MINUTE, 
SECOlqD. 
A l)eri~×l Pi is a subperiod of a pecind P iff 1" can be seen as 
consisting of a number of periods Pi that togeflmr exhaust I'. 
A phase p is a specific instance of a snbperiod having a eeltain 
order ia tire sequence of subperiods cxhaustillg a given period 
P. 
For example, a period such as YEAR can be seen as consist- 
ing of twelw+ subperiods (MONTH). January is the first phase 
of those twelve subperiods. 
The graph below illustrates the relation between year as a 
period and the monthly phases. 
'~ ........ YEAR ..... 
Fig. 1 The YEAR period 
This graph shows the year period from one point of view. We 
could split the year into other phases, for' instance, into periods 
of seasons, where summer, autumn, winter and spring would 
be the corresponding phases. Note that a sequence of phases 
is cyclically lecurring. 
Apart fi'c,m differentiating periods and phases we must be able 
to show the ,'elations between them, The following table shows 
some period:; with corresponding phases: 
YEP,R: CALENDAR {...0...} 
MONTD.: YEAR { Janmtry,...Dec ember } 
WEEK: YEAR { 1, 2, ...53 } 
DA'~(: MONTH 
(DATE) { l, 2,..31 } 
WEEK 
(I)W) {Monday,...Sunday/ 
HOUR: DAY {0, 1,...23 } 
MINUTE: HOUR {0, l, ...59} 
SECONI:): MINUTE { 0,1, ._59 } 
3 One could say that the system of numberexl weeks is similar to 
file, use of named months or named days. The analogy does not 
ho:Ld Idt the way of course as the week system is historically 
indel~mdent from the Gregoriau calendar, but we have 'tried' to 
force the week concept onto the concept of year by naming the 
weeks with numbers. In Sweden a umubered week always slarls 
on a Monday. The first week that holds at least four days of a 
new year forms week 1. Tire first of January 1987 was a qhursday 
and pint of week 1, whereas the first of January 1988 is a Friday 
which :esults in the first three days of 1988 being part of week 
53 19811 This is standardized by Swedish authorities. 
Fox each period there are one or two possibilities to view it as 
a subpefiod of a higher-level period. The difference between 
the two different ways of referring to a DAY period is shown 
by the fact that there are two subperiod-of relations, one to 
MONTH, and one to WEEK. 
The subperiod-of relations can be displayed in a temporal 
hierarchy of lhe following kind. 
YEAR 
................ ...... 
nour~of-day 
Fig. 2 The temporal hierarchy 
The lines connecting temporal periods to each other show 
subperiod-.of relations. The hierarchy shows the two diflerent 
paths fi'om YEAR to DAY. 
:The periods and phases described above share one property 
and that is that they all have fixed lengths and as a conse- 
quence clear boundaries. We can easily locate the point on the 
time axis where January becomes February, but we cannot 
with accuracy specify the location on the time axis where 
spring is succeeded by summer. So we must distinguish be- 
- tween bounded and fuzzy periods. There are other phasal divi-- 
sions one can make. For example, we could split the week into 
weekdays and non-weekdays (week-ends?), and tim year :into 
feasts, such as Christmas and Easter, and non-feasts, etc. It is 
just a matter of fact that we divide time into different temporal 
scales, and some contain periods of fixed length and some do 
not. This is why it is problematic to try and map a phase of no 
fixed length, such as summer, onto another temporal scale 
where we are dealing with fixed boundaries sueb as the one 
depicted in the temporal hierarchy above. 
Durative expressions are mostly expressed in terans of quanti-- 
fied periods: one week, two months, three years, etc. It is more 
seldom that phasal expressions are used in a durative sense. 
Quantified phasal expressions such as two mornings, six 
Thursdays, three winters, etc are primarily used to express 
habituality and iteration. It is however possible to infer dura- 
tion fl'om these as we know the length of a phase or can infer it 
from its corresponding period. 
Phasal and deictic expressions 
In accordance with the previous section we can now distinguish 
between phasal and deictic expressions. 
In our terminology a phasal expression is a temporal expres- 
sion that primarily describes a phase by using a corresponding 
word for the phase in question. A phasal expression may be, a 
single word (1988, January, midnight) or be more complex, such 
as a prepositional phrase (in 1988, in January, at midnighO. 
427 
The difference between Smith's clock calendar adverbials 
/Smith 1981/ and phasal expressions is that phasal expres- 
sions are just "providers of phases" and they are not primarily 
anchored to any other time as clock calendar adverbials are. 
Phasal expressions may describe absolute times if they refer to 
a unique phase on the time axis. So if the phasal expression 
1987 denotes a unique phase of the calendar then it is possible 
to map it into an absolute time. Following/Hinrichs 1986/we 
call these phasal expressions complete or independent dates. 
Also included in this class we find complex phasal expressions 
which, if mapped on to the temporal hierarchy, would form a 
chain of temporal information. By chain of temporal information 
we mean a chain of temporal phases according to the temporal 
hierarchy. 
Deictic expressions function basically in the following way: 
Starting from a reference time (eg. ST) a deictic will establish a 
new reference time with a different phasal value for the rele- 
vant period by moving a number of steps in either a forward (+) 
or a backward (-) direction depending on the deictic, and 
keeping phasal values for higher-level periods consistent with 
this change. 
Certain deictics do not change the reference time. For example. 
i dr (this year), den h?ir veckan (this week), i dag (today), etc, 
do not move the reference time in a forward or backward direc- 
tion. The new RT will be a partial copy of the old RT; today will 
describe a time equal to ST and specified to the DAY period 
level. 
The deictic expression n u (now) is ambiguous in respect of pe- 
riod level. In one context nu would map onto the year level and 
in another context it would refer to the hour level of RT. 
In our system the function that maps a deictic expression is of 
the form F (x, index, step) where x is either a phase or a pe- 
riod. Applying F results in a description of the time in terms of 
a set of phases which forms a chain in the temporal hierarchy 
with x as its most specific phase or period. Posterior deictics 
will have positive numbers as step, anterior will have negative 
numbers and simultaneous will have 0. For example, a deictic 
such as i morgan (tomorrow) will be mapped to a set of corre- 
sponding phases from the YEAR period down to the DAY pe- 
riod, leaving more specific phases unspecified. This means that 
while constructing a description of a time unnecessary work is 
avoided as we are dealing with partial descriptions and not the 
temporal objects as such. Compare the following two phrases: 
(1) tomorrow 
(2) tomorrow at 3 o'clock. 
In both expressions tomorrow will contribute with exactly the 
same information, ie. a description of a certain day of a certain 
month in a certain year, etc. 
Deictics in Swedish can be categorically characterized in the 
following way: 
". Lexical deicties (such as igdr (yesterday), fjol (last year) 
idag (today). 
° Pre/postpositional phrases with a temporal NP where the 
pre/postposition signals the type of temporal expression. For 
example, am tvd veckor (in two weeks), f~r fem dr sedan (five 
years ago). 
- Noun phrases with a temporal phase or period word as head 
and a modifier or ordinal that signals a deictic function, such as 
(n?ista vecka (next week), f~rra dret (last year), etc. 
In many contexts prepositions are omitted in Swedish deictic 
expressions if the remaining NP signals a deictic function on its 
own. 
428 
Note also that a phasal expression such as in October may, 
apart from specifying a phase October, also function deictically, 
that is, it may provide phasal values for the periods above its 
explicit level. However, this is regarded as a secondary use of 
a phasal expression. 
Determining the initial reference time (or index) for deictic 
expressions is another important consideration. Some deictic 
expressions are necessarily anchored to ST and others may be 
anchored to ST but they may also be anchored to another 
reference time depending on context. In Swedish expressions 
such as igdr (yesterday), i morgan (tomorrow), am 2 dagar (in 
two days) and fSrra dret (last year) are examples of 
expressions that must anchor to ST. Some expressions in- 
volving ndsta (next) are examples of the second group. The 
expressions ndista vecka (next week) and nd~sta torsdag (next 
Thursday) can have either ST or another context-dependent 
time as their initial reference time. Expressions such as ndista 
dag (next day.) and tvd veckor senate (two weeks later) must 
necessarily anchor to a reference time other than ST (see 
/Merkel 1987/. 
Next-expressions 
Expressions such as ndsta torsdag (next Thursday), ndista 
sommar (next summer) and n~ista jul (next Christmas) may be 
ambiguous to certain speakers. These expressions seem to be 
ambiguous in the sense that they either take you 1 or 2 steps 
from your reference time. So ntista torsdag may refer to the first 
or second Thursday from the initial reference time. If we 
changed the argument of ndsta in the above examples to words 
denoting periods instead of phases the corresponding reference 
times would not be ambiguous. Ntt'sta vecka (next week) and 
n?ista dag (next day) will be interpreted as having only one 
temporal location and not two as the first examples. How is 
this possible? 
If somebody says ntista torsdag (next Thursday) when the ini- 
tial reference time is a Thursday, then there is no ambiguity; 
the step value will be +1 which will pick out the first phase that 
has the value torsdag after the initial RT. However, if ntista 
torsdag was uttered on a Sunday, we would have to adjust the 
initial RT by either starting at the Thursday preceding the ini- 
tial RT orat the Thursday succeeding it, and from the 'new' ini- 
tial RT move +1 to reach a temporal reference. The expression 
nasta jul (next Christmas) is analogous to nasta torsdag. 
Instead of saying that next-expressions have two possible 
step values, +1 or +2, we claim that there is only one value, 
namely +1, but that when the argument is a phasal expression, 
such as torsdag, the initial RT may be chosen in two ways de- 
pending on individual strategies. Some may for example choose 
the nearest phase as their new RT. 
There is a class of expressions that behaves tl~e same way as 
next-expressions, for example, expressions involving modifiers 
such as fSrra (~ last), nastnasta (the next but one). 
Interpretation principle 
By looking at the properties of the different parts of a complex 
temporal expression interpretation principles for frame-adver- 
bial expressions can now be set up. Making use of the distinc- 
tion between the deietic and phasal expressions together with 
the temporal hierarchy we can outline a Frame-adverbial 
interpretation principle which will explain when a frame-adver- 
bial expression is interpretable: 
It is possible to interpret a temporal frmne-adverbial phrase au- 
tanomcusly iff 
1. a) \] he phrase consist8 of olin or several phasal expressions 
and 
b) 't'he eombimttion of phasal values wilt constitut~ a chain of 
1,3mpot-al infonnafi(m according to the icmpmal hierarchy. 
and 
c) ')'he top-most phase of the chain specifies a unique phase. 
or 
2. a) 'Yhe phrase con~;ists of a combhlation of one or several deieties 
and an arbitrtay numbes of phasal expressions 
and 
b) hMex is lmown for each deictic 
~mt~ 
e) 'the deietics and the phasal expressions each specify consistent 
phase-of relations. The phasal values provided will constitnte a 
ch~,in of temlm~al infommtion according to rim tcmlmmI 
hierarchy. 
IRt( ( 
d) A ddctic provides tonporal information for the highest 
level of the chain. 
The abow: principle will permit intc~pretation of expressions 
such as 
O) 
(2) 
1987 i maj 
den 24 maj 1987 
i mo/gon kl kvart Over' fyra 
ngtsh~ reeks pd torsdag kl 
.~vart 6vet fyra 
for 20 dr sedan idag 
rid den htir tiden i morgon 
1987 in May 
May 24th, 1987 
tomorrow at a quartet' past four 
~ext week on l"hursday at 
a quarter past four 
20 years ago today 
at this time tomorrow 
fSr 39 dr" och fyra t*~m~der sedaza 39 years and four ~umths ago 
om t,M veckor oeh fyra dagar in two weeks and four days 
The following expressions will be ruleA out by the principle: 
(3) kl kvart i~ver 5 1987 at a q~tarter past Jive 1987 
pd kvdllen i jnnua~i in the evening in Januacy 
(4) fOrra dret pd eftermiddagen last year in the afternoon 
nasta recks k112 next week at nvelve o' clock 
The fact that an expression i.,; ruled out by the principle does 
not mean that into'pretation is blocked completely. The ex- 
pressions in (3) and (4) are only incomplete in the sense that 
some perk,ds lack a phasal value and it may turn out that con- 
textual knowledge will provide this. Inteq~retation is stack if 
the expression yields inconsistent phasal values. For example, 
the expression pd mdndagen den 23 november i dr (on Momqay 
Novembe~ 23rd this year) provides inconsistent phasal values 
for the I)AY period, ie. November 23rd i,~ a Wednesday in 
1988. 
However, there are some borderline cases that the above 
principle would permit such a,q 
(5) for .39 dr sedan ig& 
n~'~a reeks n&~ta dr 
for 2 ar sedan fOr 2 nu~uuler sedan 
(6) for 39 & sedan i ~u~rgon 
om s,.x dr fOr 2 mdnader se&m 
39 ),ears ago yesterday 
next week next year 
two years ago two months ago 
39 year's ago tomorrow 
in six years 2 months ago 
\[n (5) two deictics with the same direction are combined, either 
+ +, or .... . And in (6) there is a combination of deictics with 
different relational values, that is an anterior is joined with a 
posterior deictic. In principle it seems possible to combine de-- 
ictics in this way, although some Swedish speakers do con-. 
sider the examples in (5) and (6) as being odd. 
The examples in (5) and (6) are all complex frame-adverllial 
expression holding more than one deictic phrase, but the im-- 
portant thing is that the different deictics together specify the 
same tinre. In other words, if we interpret a phrase such as 
(7)fiOr tvd dr sedan igdr (two years ago yesterday) 
where the two involved deictics both have ST as obligatory in- 
dex the first deietic will pick out a description of a reference 
time two years before ST and the second will modify that de- 
scription by adding phases for DAY and MONTH based on the 
partial description of a phase one day before ST. This view 
makes it possible to claim that certain deictics such as igdr 
(yesterday), i morgon (tomorrow), ete, always have ST as 
their index. /Smith 1978/ has proposed that interpretation of 
expressions such as (7) is done in two steps, that is, that the 
first deictic forms the RT for tile second. Smith's strategy would 
mean that igdr (yesterday) in (7) cannot have ST as its obli- 
gatory index; with our strategy this is indeed possible. 
hnplementations 
The principles outlined for the interpretation of temporal I~'amc- 
adverbials have been implemented in a system, CLOCKWISE, 
which interprets frame-adverbial expressions into a temporal 
description in terms of phasal wdues. Tht: first version of 
CI,OCKWISE consists of a parser, based on finite ~';tatc ma- 
chinery, and a 'temporal expert' that will make use of its 
knowledge about temporal phases and periods and infer tem- 
poral information that is missing explicitly in the expressicms. 
A temporal representation is constructed in a notepad dm'ing 
the parsing process. The notepad contains information about 
the periods and phases denoted by the expression and~ if the 
expression is deictic, also index, step value and direction. Thc 
notepad is structured according to the temporal hierarchy and 
will therefore support the interpreter according to the 
l,lterpretation principle. The first version can, however, only 
deal with one type of index, namely speech time. CI_,OCKWISI-!, 
1 has been usexl as a module in a natural language and graphi-- 
cal interface to a booking system/J6nsson 1987/. 
The second version of CLOCKWISE is under construction. The 
temporal representation is built by an LFG-type gimmnar to 
gether with a frame-based knowledge representation whmv 
temporal periods and phases am treated as semantic objects 
(of /Ahrenberg 1988/. The grammm" is written in a way to 
syntactically filter out file temporal expressions, ie. temporal 
prepositional phrases are functionally distinct front other 
prepositional phrases in the functional structures (f- 
structures). The result of a successful interpretation of a 
temporal frame-adverbial is a directed acyclic graph (DAG) 
where a set of phasal values forms a description of the time 
denoted by the expression. For example, a frame-adverbial 
such as niista vecka pd fredag kl 12.30 (next week on Friday at 
12.30) has a functional structure of the following kind: 
429 
TEMP 
IioLEX $WEEK \]\] RD IN.~STA\] \[ 
ASE UNM 31 
FORM UNM \]J 
\[-PCASE .,A \] 
E LEX SFREDA~ 
EGEND UTR 3 
EcAsE 
~EX {$HOUR12 $MINUTE303 
Fig. 3 Functional structure 
The above DAG is mapped to an intermediate DAG by the 
Frame system. The intermediate DAG has separated deictic 
phrases from phasal ones, and also provided a frame for the 
deictic mapping function F. 
rEaP   icT,c \] / r \]/ 
EVHASAL *"OUR12 2 
EPHASAL SMINUTE30~ 
Fig. 4 Intermediate structure 
By using a more general and powerful framework we are able 
to incorporate other types of temporal expressions and develop 
the above principles in relation to tense and aspect. Durative 
expressions have recently been incorporated in the system. 
The development of CLOCKWISE is part of the grammar 
development project in the LINLIN project at LinkSping 
University (/Ahrenberg 1987/). 
CLOCKWISE is at the moment unable to handle expressions 
such as 
(1) The first week of January 
CLOCKWISE will get stuck on this expression due to the fact 
that weeks cannot be mapped onto months, whereas the first 
day of January would result in a description. One solution 
would be to force a mapping of weeks onto months (in the 
same way as weeks are mapped onto years in the Swedish 
calendar) giving us five subperiods of MONTH each of week 
length, with corresponding phases where the first and the fifth 
week phase sometimes would be partial. 
Acknowledgements 
This research has been supported by the NationaV Swedish 
Board for Technical Development. 
I would like to thank Lars Ahrenberg, Ntis Dahlbltck, Arne 
Jtnsson, Mats Wirtn och Ivan Rankin for helpful comments on 
drafts of this paper. I am also indebted to Jim Goodwin who has 
provided me with the knowledge representation tool used in 
CLOCKWISE 2. 

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