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<!-- ! Licensed to the Apache Software Foundation (ASF) under one
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! software distributed under the License is distributed on an
! "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
! KIND, either express or implied. See the License for the
! specific language governing permissions and limitations
! under the License.
! --><h1>The Asterix Data Model (ADM)</h1>
<div class="section">
<h2><a name="Table_of_Contents"></a><a name="toc" id="toc">Table of Contents</a></h2>
<ul>
<li><a href="#PrimitiveTypes">Primitive Types</a>
<ul>
<li><a href="#PrimitiveTypesBoolean">Boolean</a></li>
<li><a href="#PrimitiveTypesInt">Tinyint / Smallint / Integer (Int) / Bigint</a></li>
<li><a href="#PrimitiveTypesFloat">Float</a></li>
<li><a href="#PrimitiveTypesDouble">Double (Double Precision)</a></li>
<li><a href="#PrimitiveTypesString">String</a></li>
<li><a href="#PrimitiveTypesBinary">Binary</a></li>
<li><a href="#PrimitiveTypesPoint">Point</a></li>
<li><a href="#PrimitiveTypesLine">Line</a></li>
<li><a href="#PrimitiveTypesRectangle">Rectangle</a></li>
<li><a href="#PrimitiveTypesCircle">Circle</a></li>
<li><a href="#PrimitiveTypesPolygon">Polygon</a></li>
<li><a href="#PrimitiveTypesDate">Date</a></li>
<li><a href="#PrimitiveTypesTime">Time</a></li>
<li><a href="#PrimitiveTypesDateTime">Datetime (Timestamp)</a></li>
<li><a href="#PrimitiveTypesDuration">Duration/Year_month_duration/Day_time_duration</a></li>
<li><a href="#PrimitiveTypesInterval">Interval</a></li>
<li><a href="#PrimitiveTypesUUID">UUID</a></li>
</ul></li>
<li><a href="#IncompleteInformationTypesTypes">Incomplete Information Types</a>
<ul>
<li><a href="#IncompleteInformationTypesNull">Null</a></li>
<li><a href="#IncompleteInformationTypesMissing">Missing</a></li>
</ul></li>
<li><a href="#DerivedTypes">Derived Types</a>
<ul>
<li><a href="#DerivedTypesObject">Object</a></li>
<li><a href="#DerivedTypesArray">Array</a></li>
<li><a href="#DerivedTypesMultiset">Multiset</a></li>
</ul></li>
</ul>
<p>An instance of Asterix data model (ADM) can be a <i><i>primitive type</i></i> (<tt>boolean</tt>, <tt>tinyint</tt>, <tt>smallint</tt>, <tt>integer</tt>, <tt>bigint</tt>, <tt>string</tt>, <tt>float</tt>, <tt>double</tt>, <tt>date</tt>, <tt>time</tt>, <tt>datetime</tt>, etc.), a <i><i>special type</i></i> (<tt>null</tt> or <tt>missing</tt>), or a <i><i>derived type</i></i>.</p>
<p>The type names are case-insensitive, e.g., both <tt>BIGINT</tt> and <tt>bigint</tt> are acceptable.</p></div>
<div class="section">
<h2><a name="Primitive_Types"></a><a name="PrimitiveTypes" id="PrimitiveTypes">Primitive Types</a></h2>
<div class="section">
<h3><a name="Boolean"></a><a name="PrimitiveTypesBoolean" id="PrimitiveTypesBoolean">Boolean</a></h3>
<p><tt>boolean</tt> data type can have one of the two values: <i><i>true</i></i> or <i><i>false</i></i>.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;true&quot;: true, &quot;false&quot;: false };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;true&quot;: true, &quot;false&quot;: false }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Tinyint__Smallint__Integer_Int__Bigint"></a><a name="PrimitiveTypesInt" id="PrimitiveTypesInt">Tinyint / Smallint / Integer (Int) / Bigint</a></h3>
<p>Integer types using 8, 16, 32, or 64 bits. The ranges of these types are:</p>
<ul>
<li><tt>tinyint</tt>: -127 to 127</li>
<li><tt>smallint</tt>: -32767 to 32767</li>
<li><tt>integer</tt>: -2147483647 to 2147483647</li>
<li><tt>bigint</tt>: -9223372036854775808 to 9223372036854775807</li>
</ul>
<p><tt>int</tt> is an abbreviated alias for integer.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;tinyint&quot;: tiny(&quot;125&quot;), &quot;smallint&quot;: smallint(&quot;32765&quot;), &quot;integer&quot;: 294967295, &quot;bigint&quot;: bigint(&quot;1700000000000000000&quot;)};
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;tinyint&quot;: 125, &quot;smallint&quot;: 32765, &quot;integer&quot;: 294967295, &quot;bigint&quot;: 17000000 }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Float"></a><a name="PrimitiveTypesFloat" id="PrimitiveTypesFloat">Float</a></h3>
<p><tt>float</tt> represents approximate numeric data values using 4 bytes. The range of a float value can be from 2^(-149) to (2-2^(-23)&#xb7;2^(127) for both positive and negative. Beyond these ranges will get <tt>INF</tt> or <tt>-INF</tt>.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: float(&quot;NaN&quot;), &quot;v2&quot;: float(&quot;INF&quot;), &quot;v3&quot;: float(&quot;-INF&quot;), &quot;v4&quot;: float(&quot;-2013.5&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: NaN, &quot;v2&quot;: Infinity, &quot;v3&quot;: -Infinity, &quot;v4&quot;: -2013.5 }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Double_double_precision"></a><a name="PrimitiveTypesDouble" id="PrimitiveTypesDouble">Double (double precision)</a></h3>
<p><tt>double</tt> represents approximate numeric data values using 8 bytes. The range of a double value can be from (2^(-1022)) to (2-2^(-52))&#xb7;2^(1023) for both positive and negative. Beyond these ranges will get <tt>INF</tt> or <tt>-INF</tt>.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: double(&quot;NaN&quot;), &quot;v2&quot;: double(&quot;INF&quot;), &quot;v3&quot;: double(&quot;-INF&quot;), &quot;v4&quot;: &quot;-2013.593823748327284&quot; };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: NaN, &quot;v2&quot;: Infinity, &quot;v3&quot;: -Infinity, &quot;v4&quot;: -2013.5938237483274 }
</pre></div></div></li>
</ul>
<p><tt>Double precision</tt> is an alias of <tt>double</tt>.</p></div>
<div class="section">
<h3><a name="String"></a><a name="PrimitiveTypesString" id="PrimitiveTypesString">String</a></h3>
<p><tt>string</tt> represents a sequence of characters. The total length of the sequence can be up to 2,147,483,648.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: string(&quot;This is a string.&quot;), &quot;v2&quot;: string(&quot;\&quot;This is a quoted string\&quot;&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: &quot;This is a string.&quot;, &quot;v2&quot;: &quot;\&quot;This is a quoted string\&quot;&quot; }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Binary"></a><a name="PrimitiveTypesBinary" id="PrimitiveTypesBinary">Binary</a></h3>
<p><tt>binary</tt> represents a sequence of bytes. It can be constructed from a <tt>hex</tt> or a <tt>base64</tt> string sequence. The total length of the byte sequence can be up to 2,147,483,648.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{
&quot;hex1&quot; : hex(&quot;ABCDEF0123456789&quot;),
&quot;hex2&quot;: hex(&quot;abcdef0123456789&quot;),
&quot;base64_1&quot; : base64(&quot;0123456789qwertyui+/&quot;),
&quot;base64_2&quot; : base64('QXN0ZXJpeA==')
};
</pre></div></div></li>
<li>
<p>The default output format is in <tt>hex</tt> format. Thus, the expected result is:</p>
<div class="source">
<div class="source">
<pre>{
&quot;hex1&quot;: hex(&quot;ABCDEF0123456789&quot;),
&quot;hex2&quot;: hex(&quot;ABCDEF0123456789&quot;),
&quot;base64_1&quot;: hex(&quot;D35DB7E39EBBF3DAB07ABB72BA2FBF&quot;),
&quot;base64_2&quot;: hex(&quot;41737465726978&quot;)
}
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Point"></a><a name="PrimitiveTypesPoint" id="PrimitiveTypesPoint">Point</a></h3>
<p><tt>point</tt> is the fundamental two-dimensional building block for spatial types. It consists of two <tt>double</tt> coordinates x and y.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: point(&quot;80.10d, -10E5&quot;), &quot;v2&quot;: point(&quot;5.10E-10d, -10E5&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: point(&quot;80.1,-1000000.0&quot;), &quot;v2&quot;: point(&quot;5.1E-10,-1000000.0&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Line"></a><a name="PrimitiveTypesLine" id="PrimitiveTypesLine">Line</a></h3>
<p><tt>line</tt> consists of two points that represent the start and the end points of a line segment.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: line(&quot;10.1234,11.1e-1 +10.2E-2,-11.22&quot;), &quot;v2&quot;: line(&quot;0.1234,-1.00e-10 +10.5E-2,-01.02&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: line(&quot;10.1234,1.11 0.102,-11.22&quot;), &quot;v2&quot;: line(&quot;0.1234,-1.0E-10 0.105,-1.02&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Rectangle"></a><a name="PrimitiveTypesRectangle" id="PrimitiveTypesRectangle">Rectangle</a></h3>
<p><tt>rectangle</tt> consists of two points that represent the <i><i>bottom left</i></i> and <i><i>upper right</i></i> corners of a rectangle.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: rectangle(&quot;5.1,11.8 87.6,15.6548&quot;), &quot;v2&quot;: rectangle(&quot;0.1234,-1.00e-10 5.5487,0.48765&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: rectangle(&quot;5.1,11.8 87.6,15.6548&quot;), &quot;v2&quot;: rectangle(&quot;0.1234,-1.0E-10 5.5487,0.48765&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Circle"></a><a name="PrimitiveTypesCircle" id="PrimitiveTypesCircle">Circle</a></h3>
<p><tt>circle</tt> consists of one point that represents the center of the circle and a radius of type <tt>double</tt>.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: circle(&quot;10.1234,11.1e-1 +10.2E-2&quot;), &quot;v2&quot;: circle(&quot;0.1234,-1.00e-10 +10.5E-2&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: circle(&quot;10.1234,1.11 0.102&quot;), &quot;v2&quot;: circle(&quot;0.1234,-1.0E-10 0.105&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Polygon"></a><a name="PrimitiveTypesPolygon" id="PrimitiveTypesPolygon">Polygon</a></h3>
<p><tt>polygon</tt> consists of <i><i>n</i></i> points that represent the vertices of a <i><i>simple closed</i></i> polygon.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{
&quot;v1&quot;: polygon(&quot;-1.2,+1.3e2 -2.14E+5,2.15 -3.5e+2,03.6 -4.6E-3,+4.81&quot;),
&quot;v2&quot;: polygon(&quot;-1.0,+10.5e2 -02.15E+50,2.5 -1.0,+3.3e3 -2.50E+05,20.15 +3.5e+2,03.6 -4.60E-3,+4.75 -2,+1.0e2 -2.00E+5,20.10 30.5,03.25 -4.33E-3,+4.75&quot;)
};
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{
&quot;v1&quot;: polygon(&quot;-1.2,130.0 -214000.0,2.15 -350.0,3.6 -0.0046,4.81&quot;),
&quot;v2&quot;: polygon(&quot;-1.0,1050.0 -2.15E50,2.5 -1.0,3300.0 -250000.0,20.15 350.0,3.6 -0.0046,4.75 -2.0,100.0 -200000.0,20.1 30.5,3.25 -0.00433,4.75&quot;) }
}
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Date"></a><a name="PrimitiveTypesDate" id="PrimitiveTypesDate">Date</a></h3>
<p><tt>date</tt> represents a time point along the Gregorian calendar system specified by the year, month and day. ASTERIX supports the date from <tt>-9999-01-01</tt> to <tt>9999-12-31</tt>.</p>
<p>A date value can be represented in two formats, extended format and basic format.</p>
<ul>
<li>Extended format is represented as <tt>[-]yyyy-mm-dd</tt> for <tt>year-month-day</tt>. Each field should be padded if there are less digits than the format specified.</li>
<li>Basic format is in the format of <tt>[-]yyyymmdd</tt>.</li>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: date(&quot;2013-01-01&quot;), &quot;v2&quot;: date(&quot;-19700101&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: date(&quot;2013-01-01&quot;), &quot;v2&quot;: date(&quot;-1970-01-01&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Time"></a><a name="PrimitiveTypesTime" id="PrimitiveTypesTime">Time</a></h3>
<p><tt>time</tt> type describes the time within the range of a day. It is represented by three fields: hour, minute and second. Millisecond field is optional as the fraction of the second field. Its extended format is as <tt>hh:mm:ss[.mmm]</tt> and the basic format is <tt>hhmmss[mmm]</tt>. The value domain is from <tt>00:00:00.000</tt> to <tt>23:59:59.999</tt>.</p>
<p>Timezone field is optional for a time value. Timezone is represented as <tt>[+|-]hh:mm</tt> for extended format or <tt>[+|-]hhmm</tt> for basic format. Note that the sign designators cannot be omitted. <tt>Z</tt> can also be used to represent the UTC local time. If no timezone information is given, it is UTC by default.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: time(&quot;12:12:12.039Z&quot;), &quot;v2&quot;: time(&quot;000000000-0800&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: time(&quot;12:12:12.039Z&quot;), &quot;v2&quot;: time(&quot;08:00:00.000Z&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Datetime_Timestamp"></a><a name="PrimitiveTypesDateTime" id="PrimitiveTypesDateTime">Datetime (Timestamp)</a></h3>
<p>A <tt>datetime</tt> value is a combination of an <tt>date</tt> and <tt>time</tt>, representing a fixed time point along the Gregorian calendar system. The value is among <tt>-9999-01-01 00:00:00.000</tt> and <tt>9999-12-31 23:59:59.999</tt>.</p>
<p>A <tt>datetime</tt> value is represented as a combination of the representation of its <tt>date</tt> part and <tt>time</tt> part, separated by a separator <tt>T</tt>. Either extended or basic format can be used, and the two parts should be the same format.</p>
<p>Millisecond field and timezone field are optional, as specified in the <tt>time</tt> type.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: datetime(&quot;2013-01-01T12:12:12.039Z&quot;), &quot;v2&quot;: datetime(&quot;-19700101T000000000-0800&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: datetime(&quot;2013-01-01T12:12:12.039Z&quot;), &quot;v2&quot;: datetime(&quot;-1970-01-01T08:00:00.000Z&quot;) }
</pre></div></div></li>
</ul>
<p><tt>timestamp</tt> is an alias of <tt>datetime</tt>.</p></div>
<div class="section">
<h3><a name="DurationYear_month_durationDay_time_duration"></a><a name="PrimitiveTypesDuration" id="PrimitiveTypesDuration">Duration/Year_month_duration/Day_time_duration</a></h3>
<p><tt>duration</tt> represents a duration of time. A duration value is specified by integers on at least one of the following fields: year, month, day, hour, minute, second, and millisecond.</p>
<p>A duration value is in the format of <tt>[-]PnYnMnDTnHnMn.mmmS</tt>. The millisecond part (as the fraction of the second field) is optional, and when no millisecond field is used, the decimal point should also be absent.</p>
<p>Negative durations are also supported for the arithmetic operations between time instance types (<tt>date</tt>, <tt>time</tt> and <tt>datetime</tt>), and is used to roll the time back for the given duration. For example <tt>date(&quot;2012-01-01&quot;) + duration(&quot;-P3D&quot;)</tt> will return <tt>date(&quot;2011-12-29&quot;)</tt>.</p>
<p>There are also two sub-duration types, namely <tt>year_month_duration</tt> and <tt>day_time_duration</tt>. <tt>year_month_duration</tt> represents only the years and months of a duration, while <tt>day_time_duration</tt> represents only the day to millisecond fields. Different from the <tt>duration</tt> type, both these two subtypes are totally ordered, so they can be used for comparison and index construction.</p>
<p>Note that a canonical representation of the duration is always returned, regardless whether the duration is in the canonical representation or not from the user&#x2019;s input. More information about canonical representation can be found from <a class="externalLink" href="http://www.w3.org/TR/xpath-functions/#canonical-dayTimeDuration">XPath dayTimeDuration Canonical Representation</a> and <a class="externalLink" href="http://www.w3.org/TR/xpath-functions/#canonical-yearMonthDuration">yearMonthDuration Canonical Representation</a>.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: duration(&quot;P100Y12MT12M&quot;), &quot;v2&quot;: duration(&quot;-PT20.943S&quot;) };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: duration(&quot;P101YT12M&quot;), &quot;v2&quot;: duration(&quot;-PT20.943S&quot;) }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Interval"></a><a name="PrimitiveTypesInterval" id="PrimitiveTypesInterval">Interval</a></h3>
<p><tt>interval</tt> represents inclusive-exclusive ranges of time. It is defined by two time point values with the same temporal type(<tt>date</tt>, <tt>time</tt> or <tt>datetime</tt>).</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{
&quot;v1&quot;: interval(date(&quot;2013-01-01&quot;), date(&quot;20130505&quot;)),
&quot;v2&quot;: interval(time(&quot;00:01:01&quot;), time(&quot;213901049+0800&quot;)),
&quot;v3&quot;: interval(datetime(&quot;2013-01-01T00:01:01&quot;), datetime(&quot;20130505T213901049+0800&quot;))
};
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{
&quot;v1&quot;: interval(date(&quot;2013-01-01&quot;), date(&quot;2013-05-05&quot;)),
&quot;v2&quot;: interval(time(&quot;00:01:01.000Z&quot;), time(&quot;13:39:01.049Z&quot;)),
&quot;v3&quot;: interval(datetime(&quot;2013-01-01T00:01:01.000Z&quot;), datetime(&quot;2013-05-05T13:39:01.049Z&quot;))
}
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="UUID"></a><a name="PrimitiveTypesUUID" id="PrimitiveTypesUUID">UUID</a></h3>
<p><tt>uuid</tt> represents a UUID value, which stands for Universally unique identifier. It is defined by a canonical format using hexadecimal text with inserted hyphen characters. (E.g.: 5a28ce1e-6a74-4201-9e8f-683256e5706f). This type is generally used to store auto-generated primary key values.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>return { &quot;v1&quot;:uuid(&quot;5c848e5c-6b6a-498f-8452-8847a2957421&quot;) }
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;v1&quot;: uuid(&quot;5c848e5c-6b6a-498f-8452-8847a2957421&quot;) }
</pre></div></div></li>
</ul></div></div>
<div class="section">
<h2><a name="Incomplete_Information_Types"></a><a name="IncompleteInformationTypes" id="IncompleteInformationTypes">Incomplete Information Types</a></h2>
<div class="section">
<h3><a name="Null"></a><a name="IncompleteInformationTypesNull" id="IncompleteInformationTypesNull">Null</a></h3>
<p><tt>null</tt> is a special value that is often used to represent an unknown value. For example, a user might not be able to know the value of a field and let it be <tt>null</tt>.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;field&quot;: null };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ &quot;field&quot;: null }
</pre></div></div></li>
</ul></div>
<div class="section">
<h3><a name="Missing"></a><a name="IncompleteInformationTypesMissing" id="IncompleteInformationTypesMissing">Missing</a></h3>
<p><tt>missing</tt> represents a missing name-value pair in a object. If the referenced field does not exist, an empty result value is returned by the query.</p>
<p>As neither the data model nor the system enforces homogeneity for datasets or collections, items in a dataset or collection can be of heterogeneous types and so a field can be present in one object and <tt>missing</tt> in another.</p>
<ul>
<li>
<p>Example:</p>
<div class="source">
<div class="source">
<pre>{ &quot;field&quot;: missing };
</pre></div></div></li>
</ul>
<ul>
<li>
<p>The expected result is:</p>
<div class="source">
<div class="source">
<pre>{ }
</pre></div></div></li>
</ul>
<p>Since a field with value <tt>missing</tt> means the field is absent, we get an empty object.</p></div></div>
<div class="section">
<h2><a name="Derived_Types"></a><a name="DerivedTypes" id="DerivedTypes">Derived Types</a></h2>
<div class="section">
<h3><a name="Object"></a><a name="DerivedTypesObject" id="DerivedTypesObject">Object</a></h3>
<p>A <tt>object</tt> contains a set of &#xfb01;elds, where each &#xfb01;eld is described by its name and type. A object type is either open or closed. Open objects can contain &#xfb01;elds that are not part of the type de&#xfb01;nition, while closed objects cannot. Syntactically, object constructors are surrounded by curly braces &#x201c;{&#x2026;}&#x201d;.</p>
<p>An example would be</p>
<div class="source">
<div class="source">
<pre> { &quot;id&quot;: 213508, &quot;name&quot;: &quot;Alice Bob&quot; }
</pre></div></div></div>
<div class="section">
<h3><a name="Array"></a><a name="DerivedTypesArray" id="DerivedTypesArray">Array</a></h3>
<p>An <tt>array</tt> is a container that holds a fixed number of values. Array constructors are denoted by brackets: &#x201c;[&#x2026;]&#x201d;.</p>
<p>An example would be</p>
<div class="source">
<div class="source">
<pre> [&quot;alice&quot;, 123, &quot;bob&quot;, null]
</pre></div></div></div>
<div class="section">
<h3><a name="Multiset"></a><a name="DerivedTypesMultiset" id="DerivedTypesMultiset">Multiset</a></h3>
<p>A <tt>multiset</tt> is a generalization of the concept of a set that, unlike a set, allows multiple instances of the multiset&#x2019;s elements. Multiset constructors are denoted by two opening curly braces followed by data and two closing curly braces, like &#x201c;{{&#x2026;}}&#x201d;.</p>
<p>An example would be</p>
<div class="source">
<div class="source">
<pre> {{&quot;hello&quot;, 9328, &quot;world&quot;, [1, 2, null]}}
</pre></div></div></div></div>
</div>
</div>
</div>
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