Formatting and parsing dateTimes as strings

When you convert a date or time into a string, a format pattern must be applied that directs the conversion. Apply the format pattern to convert a date or time into a string, or to parse a string into a date or time.

During the conversion (for example, of a dateTime into a string), a pattern or a set of tokens is replaced with the equivalent source. The following diagram shows how a pattern is used to format a dateTime source to produce a character string output.

When a string is parsed (for example, when converting the string to a dateTime), the pattern or set of tokens is used to determine which part of the target dateTime is represented by which part of the string. The following diagram shows how this is done.

Syntax

The expression pattern is defined by:

   .------------.   
   V            |   
>>---+-symbol-+-+----------------------------------------------><
     '-string-'     

Characters for formatting a dateTime as a string

The following table lists the characters that you can use in a pattern for formatting or parsing strings in relation to a dateTime. The table is followed by some notes that explain more about some of the examples in the table.

The presentation of the dateTime object depends on what symbols you specify.

• Text. If you specify four or more of the symbols, the full form is presented. If you specify less than four symbols, the short or abbreviated form, if it exists, is presented. For example, EEEE produces Monday, EEE produces Mon.
• Number. The number of characters for a numeric dateTime component must be within the bounds of the corresponding formatting symbols. Repeat the symbol to specify the minimum number of digits that are required. The maximum number of digits allowed is the upper bound for a particular symbol. For example, day in month has an upper bound of 31; therefore, a format string of d allows the values 2 or 21 to be parsed but disallows the values 32 and 210. On output, numbers are padded with zeros to the specified length. A year is a special case; see note 8 in the following list. Fractional seconds are also special case; see note 5 in the following list.
• Any characters in the pattern that are not in the ranges of ['a'..'z'] and ['A'..'Z'] are treated as quoted text. For example, characters like colon (:), comma (,), period (.), the number sign (hash or pound, #), the at sign (@), and space appear in the resulting time text even if they are not enclosed within single quotes.
• You can create formatting strings that produce unpredictable results; therefore, you must use these symbols with care. For example, if you specify dMyyyy, you cannot distinguish between day, month, and year. dMyyyy tells the broker that a minimum of one character represents the day, a minimum of one character represents the month, and four characters represent the year. Therefore, 3111999 can be interpreted as either 3/11/1999 or 31/1/1999.

ISO8601, I and T DateTime tokens

If your dateTime values comply with the ISO8601:2000 'Representation of dates and times' standard, consider using the formatting symbols I and T, which match the following subset of the ISO8601 standard.

• The restricted profile as proposed by the W3C at http://www.w3.org/TR/NOTE-datetime
• Truncated representations of calendar dates, as specified in section 5.2.1.3 of ISO8601:2000
  • Basic format (subsections c, e, and f)
  • Extended format (subsections a, b, and d)

Use the formatting symbols I and T only on their own:

• The I formatting symbol matches any dateTime string that conforms to the supported subset.
• The T formatting symbol matches any dateTime string that conforms to the supported subset that consists of a time portion only.

The following table shows how the output form relates to the logical data type.

Using the input UTC format on output

An element or attribute of logical type xsd:dateTime or xsd:time that contains a dateTime as a string can specify Coordinated Universal Time (UTC) by using either the Z symbol or time zone +00:00. On input, the MRM parser remembers the UTC format of such elements and attributes. On output, you can specify whether Z or +00:00 is displayed by using the Default DateTime Format property of the element or attribute. Alternatively, you can preserve the input UTC format by selecting the message set property Use input UTC format on output. If this property is selected, the UTC format is preserved in the output message and overrides the format that is implied by the dateTime format property.

Understanding daylight saving time and the CAST function

When the broker is running in a time zone other than GMT, it calculates the daylight saving time (DST) offset on times that are supplied to it by the CAST function. For CAST to calculate the offset correctly, the time passed into CAST must have a time zone associated with it, as a Z parameter. If no time zone is associated with the value passed, the time is converted into GMT time; it is not treated as a local time stamp.

Also, when you use CAST to cast a string to a time value, the DST offset is calculated using the current system date. To cast a string to a time variable and calculate DST for a specific date, you must also specify the date.

DECLARE castTime TIME;
SET castTime = CAST (timeValue AS TIME FORMAT timePattern)

CAST(castDate, castTime AS GMTTIMESTAMP);

Examples

The following table shows a few examples of dateTime formats.

Use within an MRM domain

In MRM it is possible to define an element that has the logical type of dateTime.

When a dateTime element is parsed, a field is created in the message tree that has the ESQL datatype of CURRENT_TIME or CURRENT_TIMESTAMP. However, the CURRENT_TIME and CURRENT_TIMESTAMP data types do not have the functionality to store timezone information, and the MRM does not adjust the time according to the input timezone and the timezone of the broker.

Although the CURRENT_TIME and CURRENT_TIMESTAMP data types cannot store timezone information, the MRM stores this information as part of the underlying field. This means that if the field is copied between message trees, the timezone information is copied with it, allowing this information to be preserved on output.

Note that the information is preserved only if the field is copied to a field of the same name.

However, if any new field is derived from the original field, the new field does not have the timezone information. This means that if such a field is cast as a character, the new field assumes the timezone of the broker, but its value is not adjusted for any difference between the input timezone and the timezone of the broker.

For example, an input dateTime element containing 2009-02-20T06:08:07-08:00 could be copied from the input message tree to the output message tree and appear in an output message in exactly the same format. However, if the element is cast as character, using format IU, by a broker running GMT the result would be 2009-02-20T06:08:07.000Z.