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Structure of Time Principal Element

5.It's About Time!(Chronological Records)

Time	Individual chronological values or ranges of values (periods)

<Time>
    <Entry
        <Year>1776</Year>
        <Month>07</Month>
        <Day>04</Day>
    </Entry>
</Time>

Time is handled homogeneously throughout XOBIS, with the obvious exception of Description. The date of publication, date of a conference, death date of an author, date qualifier in a title, creation date of a record, etc. are marked up identically. Although somewhat verbose, this provides a consistency that holds considerable potential for generalizing, and thus improving, chronological access in regard to other Principal Elements and their Relationships. While Time may be recorded without regard to the existence of a temporal authority record, a hierarchical arrangement of controlled Chronological Records with their Entry/Varia linked in a rich array of Relationships is envisioned. Some temporal values are recorded systematically in MARC, but current practice prevents catalogs from moving much beyond the simple limiting by date of publication.This is difficult to understand in view of the fundamental universality of Time.

Instantive aspects of Time differ from those of other Principal Elements. First, there are an infinite number of instants possible. Individual temporal instances or periods are identified commonly by numeric designations, e.g. 2001, instead of by proper names.However, proper names occur sporadically and vary from representing a single day (VE Day) to an entire era (the Renaissance).Regardless of duration, most ordinary temporal values are collective, e.g. a century contains years, years contain months, and so forth. It is helpful to consider that a day, an hour, etc. have a start and stop times.Lastly, all such designations are human constructs, systems of dating called calendars, each of which may be considered a Work, itself promulgated at a time related to a cosmic cyclic event, an historical event, or to another scheme. To keep things interesting, calendars overlap in a most peculiar assortment of ways.

Thus, with the goal of providing a unified treatment of dates and times in XOBIS, Time broadly represents instantiation of various calendars, individually or collectively, each preferably identified by a Work authority. Values may stand alone, although a remote goal would be to harmonize the major calendars to the extent that synonymy can be identified.After all, they all represent the same intangible.Specific values are virtual instantiations of a given Concept, e.g. the abstract solar year, or in its collective form, years. The "isness" of categorization discussed earlier applies here as well, e.g. 1948 is a Year. Whether considered "specific" or "collective", all such values are necessarily Time and may have implicit or explicit Relationships both to other values of Time and/or to Concept. Regarding relativity and extraterrestrial aspects … ☺

Time currently has a 'usage' attribute with the sole value of subdivision, to indicate that it may be used as a Subdivision in a Relationship. Its Entry has a 'class' attribute with values:individual (one value), collective (a range), and referential. There is also an optional 'calendar' attribute on Entry or Variant, discussed below, as well as a 'scheme' attribute.Attributes for 'language' and 'transliteration' are also optional.

Currently, the following options appear to handle all patterns identified to date. Fortunately, the more complex structures occur less frequently.

In all cases, Time includes either a Name or a special chronological substructure. See Figure 4 for an overview of this in context.This substructure is based on ISO 8601:2000, the International Organization for Standardization's standard for date and time (55).Its elements include:

See the schema itself for how this is used for ControlData and for treatment of time zones.XOBIS relies on XSL (XML Stylesheet Language) to render display values in accordance with the standard, e.g. the date from the introductory example should display thusly:

1776-07-04 and a time: 12:34:03

Some extensions to the standard were needed to accommodate added structural and/or qualitative factors. Basically, a temporal value may consist of one or a pair of Time elements, as shown above.Two container elements, Times and Duration, permit grouping these values to describe a "single" time (e.g. 2000/2001), or a "range" of time (e.g. 1830-1839) with a maximum of four values per instance (e.g. 1966/1967-1969/1970).Containment, unusual for a Principal Element, was structurally necessary. This organization and two additional elements, Type and Certainty discussed next, provide considerable flexibility in representing time.There are differences in applicability of this arrangement depending on whether the value(s) occur on the Principal Element Time's Entry/Varia, as part of Qualifiers anywhere, or as the target of a Relationship.

The generic Type element is currently used with Time, Times, or Duration to express implicit relationships, e.g. b. 1975, or naming, e.g. Bulk Dates for archival materials. Likewise, Certainty may indicate the degree of confidence in a value. Together, these can be used to control punctuation and labeling shown in the examples below and supplied via XSL. Implicit relationships should not be confused with the Relationships element, where birth and death dates differing from an entry's could be recorded, although this practice is questioned. The Type's 'set' attribute value is currently Temporal Type with Single understood, and Certainty's 'set' attribute is Certainty Type with Exact implied. It is necessary to use Type and Certainty at the appropriate level to avoid duplicate labels due to the repeatability of Time. Experience will dictate whether attributes would better serve here.The current method provides greater flexibility during this initial phase.

Type supports the following potential display values.Rules would need to be determined and might differ depending on whether the value is in Entry/Varia or elsewhere.Currently the Entry Substitute Code is envisioned as the value for the 'set' attribute for Type, as each of these cases is a Concept. The examples are grouped by element:

Note that only one of these Type values is necessary to effect the desired punctuation (i.e. prevent duplicate hyphens).While perhaps more common in Holdings, intermittency is supported by the repeatability of Duration, e.g. 1975-1976, 1980-1981, which is useful in relationships.

The slash/virgule is useful in displaying a range when a Time value would display with the ISO recommended hyphen in punctuation.The unusual value 1919 Feb. 11-15 (distinguished from 1919 Mar. 17-19) in a conference Qualifier could be accommodated as 1919-02-11/1919-02-15.We are continuing to study ISO display issues.

The Certainty element permits equivocation of the precise values included in Time, Times, or Duration, indicating the sureness or reliability of a particular value. It is structured like Type and also relies on XSL to provide punctuation. An attribute may replace this after we have more experience/input. Lack of Certainty implies an Exact date, although this can be explicit.

Decades, centuries, and millennia represent Certainty as well, e.g. 1860s, 1900s, and 1000s, although these often are referred to by other names, e.g. 20th century.Ordinal numbers (1st, 2nd, 3rd, nth) add considerable variety. As coded values, MARC indicates uncertainty with the filler "u", e.g. 19uu. In this situation we considered using Type with a Code,such as Decade, to indicate display of a trailing "s" on the bald whole value, e.g. 1860.Because XOBIS posits Time authorities, the many ordinal cases may be handled preferably in that context, cf. a likely named Time:

The Code can be addressed using the 'substitute' attribute on a Principal Element as a qualifier or on Duration of a Variant or Relationship.

Time has the most complex markup in XOBIS. Chronological details remain under study as some more exotic values are likely to occur. Roman numerals as dates are probably best treated as Description, although they may be additionally included as Varia for Time. We have not had time to consider geologic times adequately, although BC is handled by the 'calendar' attribute, cf. below.These techniques allow dates to be indexed by value, but displayed with trappings. An alternative would be to define 'prefix' and 'suffix' attributes similar to 'nonfiling'.This example illustrates current markup for the value: <1948>-1959?

<Duration>
    <Time> 
        <Type set="Temporal Type">Begin</Type>
        <Certainty set="Time Certainty">Temporary</Certainty>
        <Year>1948</Year>
    </Time>
    <Time>
        <Type set="Temporal Type">End</Type>
        <Certainty set="Time Certainty>Questionable</Certainty>
        <Year>1959</Year>
    </Time>
</Duration>

Because a specific calendar may apply to Entry or Variant and because a particular case only has one calendar, using an attribute worked best.The 'calendar' attribute is optional. The currently prevalent Gregorian calendar for the Common Era (CE/AD) represents a base, or default, and is omitted.Chronological Records from any calendar may standalone, e.g. 1026 FE for Asimov's fictional First Empire dating, but linking values to the Gregorian calendar as Varia when possible lends uniformity.The values of 'calendar' represent the Code on the authority for the parallel Work, and are intended to group index entries by calendar and/or BC.Due to the characteristics of ASCII, bald numeric values for Gregorian entries would file first. Some suggested codes:

Structuring a chronological index would take advantage of the hierarchical nature of values for the chronological "names" of Entry/Varia, cf. Figure 4. This example suggests the underpinning arrangement and indicates some textual Varia on the right:

1900-1999			20th Century20th Cent. 1900s
Related:	2000
Earlier:	1800-1899		19th Century
Later:	2000-2999		21st Century
Narrower:
	1900-1909
	1910-1919
	1920-1929		Roaring Twenties
		1920
		1921
		1922
		…
	1930-1939
	…

The pattern continues as individual years have earlier and later Relationships, and are composed of individual dates, e.g. 1948-01-02, continued by 1948-01-03. Records to populate this structure could be built algorithmically and/or added gradually when considered significant. With increasing granularity the need is sporadic.Cusp problems appear solvable.

Entry/Varia for Time may also have a textual Name. Whether a chronological or textual name should be the Entry remains in question.These examples indicate selected Varia and Relationships, and treat text as Entry in contrast to the above example:

Various temporal issues remain for interpretation within XOBIS' framework. Time differs from Event, which occupies time, but refers primarily to the occurrence (what happened) rather than the time period itself (when it happened).Anniversaries of events (e.g. Juneteenth), holidays (e.g. Labor Day is the first Monday in September), zodiacal signs (e.g. Capricorn), Chinese horoscopic terms (Year of the Horse), etc. are under review. Holidays and other named periods may also vary by Place. Entries not subordinate to years must rely on indexing convention; it is anticipated they would file preceding any specific year.Three examples:

Note:The coded values would not contain leading zeros; these are part of display. Displaying the range for Spring as a Variant as in the other two examples is problematic, and thus shown as two cases of Relationship.

Special days, weeks, years, decades, etc. sometimes bear proper names. An initial review of some LCSH headings used as umbrella terms suggests that some may represent a single Time (e.g. National Recycling Day = 1992-04-15) or actually indicate a topical Concept. Gay Pride Day is collective, including Gay Pride Week, etc. and might better be expressed as Gay Pride Events, which in turn could be instantiated by specific individual named Events as needed.Whether or not the International Year of the Ocean is synonymous with 1998 is questionable. Such names tend to function as a temporal umbrella for various named or unnamed activities and events. Policies would need to be refined.

Relationships of all sorts may be chronological, and Time relates to other Principal Elements.The Concept Leap Year could have a categorical link to each applicable Year. Named generations (Being) reference definable periods.The Organization America Recycles Day, Inc. may merit a Relationship. Increased use of Relationships lessens the need for Description. Consider the maritime example of a ship (Object), which may have dates of delivery, keel laying, launch, commissioning, recommissioning, decommissioning, transfer, etc.See the Relationships section for scope.