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				95	<h1>The Asterix Data Model (ADM)</h1>
				96	<div class="section">
				97	<h2><a name="Table_of_Contents"></a><a name="toc" id="toc">Table of Contents</a></h2>
				98	<ul>
				99
				100	<li><a href="#PrimitiveTypes">Primitive Types</a>
				101	<ul>
				102
				103	<li><a href="#PrimitiveTypesBoolean">Boolean</a></li>
				104	<li><a href="#PrimitiveTypesString">String</a></li>
				105	<li><a href="#PrimitiveTypesInt">Tinyint / Smallint / Integer (Int) / Bigint</a></li>
				106	<li><a href="#PrimitiveTypesFloat">Float</a></li>
				107	<li><a href="#PrimitiveTypesDouble">Double (Double Precision)</a></li>
				108	<li><a href="#PrimitiveTypesBinary">Binary</a></li>
				109	<li><a href="#PrimitiveTypesPoint">Point</a></li>
				110	<li><a href="#PrimitiveTypesLine">Line</a></li>
				111	<li><a href="#PrimitiveTypesRectangle">Rectangle</a></li>
				112	<li><a href="#PrimitiveTypesCircle">Circle</a></li>
				113	<li><a href="#PrimitiveTypesPolygon">Polygon</a></li>
				114	<li><a href="#PrimitiveTypesDate">Date</a></li>
				115	<li><a href="#PrimitiveTypesTime">Time</a></li>
				116	<li><a href="#PrimitiveTypesDateTime">Datetime (Timestamp)</a></li>
				117	<li><a href="#PrimitiveTypesDuration">Duration/Year_month_duration/Day_time_duration</a></li>
				118	<li><a href="#PrimitiveTypesInterval">Interval</a></li>
				119	<li><a href="#PrimitiveTypesUUID">UUID</a></li>
				120	</ul>
				121	</li>
				122	<li><a href="#IncompleteInformationTypes">Incomplete Information Types</a>
				123	<ul>
				124
				125	<li><a href="#IncompleteInformationTypesNull">Null</a></li>
				126	<li><a href="#IncompleteInformationTypesMissing">Missing</a></li>
				127	</ul>
				128	</li>
				129	<li><a href="#DerivedTypes">Derived Types</a>
				130	<ul>
				131
				132	<li><a href="#DerivedTypesObject">Object</a></li>
				133	<li><a href="#DerivedTypesArray">Array</a></li>
				134	<li><a href="#DerivedTypesMultiset">Multiset</a></li>
				135	</ul>
				136	</li>
				137	</ul>
				138	<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>
				139	<p>The type names are case-insensitive, e.g., both <tt>BIGINT</tt> and <tt>bigint</tt> are acceptable.</p><!--
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				141	! or more contributor license agreements. See the NOTICE file
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				144	! to you under the Apache License, Version 2.0 (the
				145	! "License"); you may not use this file except in compliance
				146	! with the License. You may obtain a copy of the License at
				147	!
				148	! http://www.apache.org/licenses/LICENSE-2.0
				149	!
				150	! Unless required by applicable law or agreed to in writing,
				151	! software distributed under the License is distributed on an
				152	! "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
				153	! KIND, either express or implied. See the License for the
				154	! specific language governing permissions and limitations
				155	! under the License.
				156	!-->
				157	</div>
				158	<div class="section">
				159	<h2><a name="Primitive_Types"></a><a name="PrimitiveTypes" id="PrimitiveTypes">Primitive Types</a></h2>
				160	<div class="section">
				161	<h3><a name="Boolean"></a><a name="PrimitiveTypesBoolean" id="PrimitiveTypesBoolean">Boolean</a></h3>
				162	<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>
				163	<ul>
				164
				165	<li>
				166
				167	<p>Example:</p>
				168
				169	<div>
				170	<div>
				171	<pre class="source">{ "true": true, "false": false };
				172	</pre></div></div>
				173	</li>
				174	<li>
				175
				176	<p>The expected result is:</p>
				177
				178	<div>
				179	<div>
				180	<pre class="source">{ "true": true, "false": false }
				181	</pre></div></div>
				182	</li>
				183	</ul></div>
				184	<div class="section">
				185	<h3><a name="String"></a><a name="PrimitiveTypesString" id="PrimitiveTypesString">String</a></h3>
				186	<p><tt>string</tt> represents a sequence of characters. The total length of the sequence can be up to 2,147,483,648.</p>
				187	<ul>
				188
				189	<li>
				190
				191	<p>Example:</p>
				192
				193	<div>
				194	<div>
				195	<pre class="source">{ "v1": string("This is a string."), "v2": string("\"This is a quoted string\"") };
				196	</pre></div></div>
				197	</li>
				198	<li>
				199
				200	<p>The expected result is:</p>
				201
				202	<div>
				203	<div>
				204	<pre class="source">{ "v1": "This is a string.", "v2": "\"This is a quoted string\"" }
				205	</pre></div></div>
				206	</li>
				207	</ul><!--
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				209	! or more contributor license agreements. See the NOTICE file
				210	! distributed with this work for additional information
				211	! regarding copyright ownership. The ASF licenses this file
				212	! to you under the Apache License, Version 2.0 (the
				213	! "License"); you may not use this file except in compliance
				214	! with the License. You may obtain a copy of the License at
				215	!
				216	! http://www.apache.org/licenses/LICENSE-2.0
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				219	! software distributed under the License is distributed on an
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				222	! specific language governing permissions and limitations
				223	! under the License.
				224	!-->
				225	</div>
				226	<div class="section">
				227	<h3><a name="Tinyint_.2F_Smallint_.2F_Integer_.28Int.29_.2F_Bigint"></a><a name="PrimitiveTypesInt" id="PrimitiveTypesInt">Tinyint / Smallint / Integer (Int) / Bigint</a></h3>
				228	<p>Integer types using 8, 16, 32, or 64 bits. The ranges of these types are:</p>
				229	<ul>
				230
				231	<li><tt>tinyint</tt>: -128 to 127</li>
				232	<li><tt>smallint</tt>: -32768 to 32767</li>
				233	<li><tt>integer</tt>: -2147483648 to 2147483647</li>
				234	<li><tt>bigint</tt>: -9223372036854775808 to 9223372036854775807</li>
				235	</ul>
				236	<p><tt>int</tt> is an abbreviated alias for integer.</p>
				237	<ul>
				238
				239	<li>
				240
				241	<p>Example:</p>
				242
				243	<div>
				244	<div>
				245	<pre class="source">{ "tinyint": tiny("125"), "smallint": smallint("32765"), "integer": 294967295, "bigint": bigint("1700000000000000000")};
				246	</pre></div></div>
				247	</li>
				248	<li>
				249
				250	<p>The expected result is:</p>
				251
				252	<div>
				253	<div>
				254	<pre class="source">{ "tinyint": 125, "smallint": 32765, "integer": 294967295, "bigint": 1700000000000000000 }
				255	</pre></div></div>
				256	</li>
				257	</ul></div>
				258	<div class="section">
				259	<h3><a name="Float"></a><a name="PrimitiveTypesFloat" id="PrimitiveTypesFloat">Float</a></h3>
				260	<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)·2^(127) for both positive and negative. Beyond these ranges will get <tt>INF</tt> or <tt>-INF</tt>.</p>
				261	<ul>
				262
				263	<li>
				264
				265	<p>Example:</p>
				266
				267	<div>
				268	<div>
				269	<pre class="source">{ "v1": float("NaN"), "v2": float("INF"), "v3": float("-INF"), "v4": float("-2013.5") };
				270	</pre></div></div>
				271	</li>
				272	<li>
				273
				274	<p>The expected result is:</p>
				275
				276	<div>
				277	<div>
				278	<pre class="source">{ "v1": "NaN", "v2": "INF", "v3": "-INF", "v4": -2013.5 }
				279	</pre></div></div>
				280	</li>
				281	</ul></div>
				282	<div class="section">
				283	<h3><a name="Double_.28double_precision.29"></a><a name="PrimitiveTypesDouble" id="PrimitiveTypesDouble">Double (double precision)</a></h3>
				284	<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))·2^(1023) for both positive and negative. Beyond these ranges will get <tt>INF</tt> or <tt>-INF</tt>.</p>
				285	<ul>
				286
				287	<li>
				288
				289	<p>Example:</p>
				290
				291	<div>
				292	<div>
				293	<pre class="source">{ "v1": double("NaN"), "v2": double("INF"), "v3": double("-INF"), "v4": "-2013.593823748327284" };
				294	</pre></div></div>
				295	</li>
				296	<li>
				297
				298	<p>The expected result is:</p>
				299
				300	<div>
				301	<div>
				302	<pre class="source">{ "v1": "NaN", "v2": "INF", "v3": "-INF", "v4": -2013.5938237483274 }
				303	</pre></div></div>
				304	</li>
				305	</ul>
				306	<p><tt>Double precision</tt> is an alias of <tt>double</tt>.</p></div>
				307	<div class="section">
				308	<h3><a name="Binary"></a><a name="PrimitiveTypesBinary" id="PrimitiveTypesBinary">Binary</a></h3>
				309	<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>
				310	<ul>
				311
				312	<li>
				313
				314	<p>Example:</p>
				315
				316	<div>
				317	<div>
				318	<pre class="source">{
				319	"hex1" : hex("ABCDEF0123456789"),
				320	"hex2": hex("abcdef0123456789"),
				321	"base64_1" : base64("0123456789qwertyui+/"),
				322	"base64_2" : base64('QXN0ZXJpeA==')
				323	};
				324	</pre></div></div>
				325	</li>
				326	<li>
				327
				328	<p>The default output format is in <tt>hex</tt> format. Thus, the expected result is:</p>
				329
				330	<div>
				331	<div>
				332	<pre class="source">{
				333	"hex1": hex("ABCDEF0123456789"),
				334	"hex2": hex("ABCDEF0123456789"),
				335	"base64_1": hex("D35DB7E39EBBF3DAB07ABB72BA2FBF"),
				336	"base64_2": hex("41737465726978")
				337	}
				338	</pre></div></div>
				339	</li>
				340	</ul></div>
				341	<div class="section">
				342	<h3><a name="Point"></a><a name="PrimitiveTypesPoint" id="PrimitiveTypesPoint">Point</a></h3>
				343	<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>
				344	<ul>
				345
				346	<li>
				347
				348	<p>Example:</p>
				349
				350	<div>
				351	<div>
				352	<pre class="source">{ "v1": point("80.10d, -10E5"), "v2": point("5.10E-10d, -10E5") };
				353	</pre></div></div>
				354	</li>
				355	<li>
				356
				357	<p>The expected result is:</p>
				358
				359	<div>
				360	<div>
				361	<pre class="source">{ "v1": point("80.1,-1000000.0"), "v2": point("5.1E-10,-1000000.0") }
				362	</pre></div></div>
				363	</li>
				364	</ul></div>
				365	<div class="section">
				366	<h3><a name="Line"></a><a name="PrimitiveTypesLine" id="PrimitiveTypesLine">Line</a></h3>
				367	<p><tt>line</tt> consists of two points that represent the start and the end points of a line segment.</p>
				368	<ul>
				369
				370	<li>
				371
				372	<p>Example:</p>
				373
				374	<div>
				375	<div>
				376	<pre class="source">{ "v1": line("10.1234,11.1e-1 +10.2E-2,-11.22"), "v2": line("0.1234,-1.00e-10 +10.5E-2,-01.02") };
				377	</pre></div></div>
				378	</li>
				379	<li>
				380
				381	<p>The expected result is:</p>
				382
				383	<div>
				384	<div>
				385	<pre class="source">{ "v1": line("10.1234,1.11 0.102,-11.22"), "v2": line("0.1234,-1.0E-10 0.105,-1.02") }
				386	</pre></div></div>
				387	</li>
				388	</ul></div>
				389	<div class="section">
				390	<h3><a name="Rectangle"></a><a name="PrimitiveTypesRectangle" id="PrimitiveTypesRectangle">Rectangle</a></h3>
				391	<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>
				392	<ul>
				393
				394	<li>
				395
				396	<p>Example:</p>
				397
				398	<div>
				399	<div>
				400	<pre class="source">{ "v1": rectangle("5.1,11.8 87.6,15.6548"), "v2": rectangle("0.1234,-1.00e-10 5.5487,0.48765") };
				401	</pre></div></div>
				402	</li>
				403	<li>
				404
				405	<p>The expected result is:</p>
				406
				407	<div>
				408	<div>
				409	<pre class="source">{ "v1": rectangle("5.1,11.8 87.6,15.6548"), "v2": rectangle("0.1234,-1.0E-10 5.5487,0.48765") }
				410	</pre></div></div>
				411	</li>
				412	</ul></div>
				413	<div class="section">
				414	<h3><a name="Circle"></a><a name="PrimitiveTypesCircle" id="PrimitiveTypesCircle">Circle</a></h3>
				415	<p><tt>circle</tt> consists of one point that represents the center of the circle and a radius of type <tt>double</tt>.</p>
				416	<ul>
				417
				418	<li>
				419
				420	<p>Example:</p>
				421
				422	<div>
				423	<div>
				424	<pre class="source">{ "v1": circle("10.1234,11.1e-1 +10.2E-2"), "v2": circle("0.1234,-1.00e-10 +10.5E-2") };
				425	</pre></div></div>
				426	</li>
				427	<li>
				428
				429	<p>The expected result is:</p>
				430
				431	<div>
				432	<div>
				433	<pre class="source">{ "v1": circle("10.1234,1.11 0.102"), "v2": circle("0.1234,-1.0E-10 0.105") }
				434	</pre></div></div>
				435	</li>
				436	</ul></div>
				437	<div class="section">
				438	<h3><a name="Polygon"></a><a name="PrimitiveTypesPolygon" id="PrimitiveTypesPolygon">Polygon</a></h3>
				439	<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>
				440	<ul>
				441
				442	<li>
				443
				444	<p>Example:</p>
				445
				446	<div>
				447	<div>
				448	<pre class="source">{
				449	"v1": polygon("-1.2,+1.3e2 -2.14E+5,2.15 -3.5e+2,03.6 -4.6E-3,+4.81"),
				450	"v2": polygon("-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")
				451	};
				452	</pre></div></div>
				453	</li>
				454	<li>
				455
				456	<p>The expected result is:</p>
				457
				458	<div>
				459	<div>
				460	<pre class="source">{
				461	"v1": polygon("-1.2,130.0 -214000.0,2.15 -350.0,3.6 -0.0046,4.81"),
				462	"v2": polygon("-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") }
				463	}
				464	</pre></div></div>
				465	</li>
				466	</ul></div>
				467	<div class="section">
				468	<h3><a name="Date"></a><a name="PrimitiveTypesDate" id="PrimitiveTypesDate">Date</a></h3>
				469	<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>
				470	<p>A date value can be represented in two formats, extended format and basic format.</p>
				471	<ul>
				472
				473	<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>
				474	<li>Basic format is in the format of <tt>[-]yyyymmdd</tt>.</li>
				475	<li>
				476
				477	<p>Example:</p>
				478
				479	<div>
				480	<div>
				481	<pre class="source">{ "v1": date("2013-01-01"), "v2": date("-19700101") };
				482	</pre></div></div>
				483	</li>
				484	<li>
				485
				486	<p>The expected result is:</p>
				487
				488	<div>
				489	<div>
				490	<pre class="source">{ "v1": date("2013-01-01"), "v2": date("-1970-01-01") }
				491	</pre></div></div>
				492	</li>
				493	</ul></div>
				494	<div class="section">
				495	<h3><a name="Time"></a><a name="PrimitiveTypesTime" id="PrimitiveTypesTime">Time</a></h3>
				496	<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>
				497	<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>
				498	<ul>
				499
				500	<li>
				501
				502	<p>Example:</p>
				503
				504	<div>
				505	<div>
				506	<pre class="source">{ "v1": time("12:12:12.039Z"), "v2": time("000000000-0800") };
				507	</pre></div></div>
				508	</li>
				509	<li>
				510
				511	<p>The expected result is:</p>
				512
				513	<div>
				514	<div>
				515	<pre class="source">{ "v1": time("12:12:12.039Z"), "v2": time("08:00:00.000Z") }
				516	</pre></div></div>
				517	</li>
				518	</ul></div>
				519	<div class="section">
				520	<h3><a name="Datetime_.28Timestamp.29"></a><a name="PrimitiveTypesDateTime" id="PrimitiveTypesDateTime">Datetime (Timestamp)</a></h3>
				521	<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>
				522	<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>
				523	<p>Millisecond field and timezone field are optional, as specified in the <tt>time</tt> type.</p>
				524	<ul>
				525
				526	<li>
				527
				528	<p>Example:</p>
				529
				530	<div>
				531	<div>
				532	<pre class="source">{ "v1": datetime("2013-01-01T12:12:12.039Z"), "v2": datetime("-19700101T000000000-0800") };
				533	</pre></div></div>
				534	</li>
				535	<li>
				536
				537	<p>The expected result is:</p>
				538
				539	<div>
				540	<div>
				541	<pre class="source">{ "v1": datetime("2013-01-01T12:12:12.039Z"), "v2": datetime("-1970-01-01T08:00:00.000Z") }
				542	</pre></div></div>
				543	</li>
				544	</ul>
				545	<p><tt>timestamp</tt> is an alias of <tt>datetime</tt>.</p></div>
				546	<div class="section">
				547	<h3><a name="Duration.2FYear_month_duration.2FDay_time_duration"></a><a name="PrimitiveTypesDuration" id="PrimitiveTypesDuration">Duration/Year_month_duration/Day_time_duration</a></h3>
				548	<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>
				549	<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>
				550	<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("2012-01-01") + duration("-P3D")</tt> will return <tt>date("2011-12-29")</tt>.</p>
				551	<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>
				552	<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’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>
				553	<ul>
				554
				555	<li>
				556
				557	<p>Example:</p>
				558
				559	<div>
				560	<div>
				561	<pre class="source">{ "v1": duration("P100Y12MT12M"), "v2": duration("-PT20.943S") };
				562	</pre></div></div>
				563	</li>
				564	<li>
				565
				566	<p>The expected result is:</p>
				567
				568	<div>
				569	<div>
				570	<pre class="source">{ "v1": duration("P101YT12M"), "v2": duration("-PT20.943S") }
				571	</pre></div></div>
				572	</li>
				573	</ul></div>
				574	<div class="section">
				575	<h3><a name="Interval"></a><a name="PrimitiveTypesInterval" id="PrimitiveTypesInterval">Interval</a></h3>
				576	<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>
				577	<ul>
				578
				579	<li>
				580
				581	<p>Example:</p>
				582
				583	<div>
				584	<div>
				585	<pre class="source">{
				586	"v1": interval(date("2013-01-01"), date("20130505")),
				587	"v2": interval(time("00:01:01"), time("213901049+0800")),
				588	"v3": interval(datetime("2013-01-01T00:01:01"), datetime("20130505T213901049+0800"))
				589	};
				590	</pre></div></div>
				591	</li>
				592	<li>
				593
				594	<p>The expected result is:</p>
				595
				596	<div>
				597	<div>
				598	<pre class="source">{
				599	"v1": interval(date("2013-01-01"), date("2013-05-05")),
				600	"v2": interval(time("00:01:01.000Z"), time("13:39:01.049Z")),
				601	"v3": interval(datetime("2013-01-01T00:01:01.000Z"), datetime("2013-05-05T13:39:01.049Z"))
				602	}
				603	</pre></div></div>
				604	</li>
				605	</ul></div>
				606	<div class="section">
				607	<h3><a name="UUID"></a><a name="PrimitiveTypesUUID" id="PrimitiveTypesUUID">UUID</a></h3>
				608	<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>
				609	<ul>
				610
				611	<li>
				612
				613	<p>Example:</p>
				614
				615	<div>
				616	<div>
				617	<pre class="source">return { "v1":uuid("5c848e5c-6b6a-498f-8452-8847a2957421") }
				618	</pre></div></div>
				619	</li>
				620	<li>
				621
				622	<p>The expected result is:</p>
				623
				624	<div>
				625	<div>
				626	<pre class="source">{ "v1": uuid("5c848e5c-6b6a-498f-8452-8847a2957421") }
				627	</pre></div></div>
				628	</li>
				629	</ul><!--
				630	! Licensed to the Apache Software Foundation (ASF) under one
				631	! or more contributor license agreements. See the NOTICE file
				632	! distributed with this work for additional information
				633	! regarding copyright ownership. The ASF licenses this file
				634	! to you under the Apache License, Version 2.0 (the
				635	! "License"); you may not use this file except in compliance
				636	! with the License. You may obtain a copy of the License at
				637	!
				638	! http://www.apache.org/licenses/LICENSE-2.0
				639	!
				640	! Unless required by applicable law or agreed to in writing,
				641	! software distributed under the License is distributed on an
				642	! "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
				643	! KIND, either express or implied. See the License for the
				644	! specific language governing permissions and limitations
				645	! under the License.
				646	!-->
				647	</div></div>
				648	<div class="section">
				649	<h2><a name="Incomplete_Information_Types"></a><a name="IncompleteInformationTypes" id="IncompleteInformationTypes">Incomplete Information Types</a></h2>
				650	<div class="section">
				651	<h3><a name="Null"></a><a name="IncompleteInformationTypesNull" id="IncompleteInformationTypesNull">Null</a></h3>
				652	<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>
				653	<ul>
				654
				655	<li>
				656
				657	<p>Example:</p>
				658
				659	<div>
				660	<div>
				661	<pre class="source">{ "field": null };
				662	</pre></div></div>
				663	</li>
				664	<li>
				665
				666	<p>The expected result is:</p>
				667
				668	<div>
				669	<div>
				670	<pre class="source">{ "field": null }
				671	</pre></div></div>
				672	</li>
				673	</ul></div>
				674	<div class="section">
				675	<h3><a name="Missing"></a><a name="IncompleteInformationTypesMissing" id="IncompleteInformationTypesMissing">Missing</a></h3>
				676	<p><tt>missing</tt> indicates that a name-value pair is missing from an object. If a missing name-value pair is accessed, an empty result value is returned by the query.</p>
				677	<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>
				678	<ul>
				679
				680	<li>
				681
				682	<p>Example:</p>
				683
				684	<div>
				685	<div>
				686	<pre class="source">{ "field": missing };
				687	</pre></div></div>
				688	</li>
				689	<li>
				690
				691	<p>The expected result is:</p>
				692
				693	<div>
				694	<div>
				695	<pre class="source">{ }
				696	</pre></div></div>
				697	</li>
				698	</ul>
				699	<p>Since a field with value <tt>missing</tt> means the field is absent, we get an empty object.</p><!--
				700	! Licensed to the Apache Software Foundation (ASF) under one
				701	! or more contributor license agreements. See the NOTICE file
				702	! distributed with this work for additional information
				703	! regarding copyright ownership. The ASF licenses this file
				704	! to you under the Apache License, Version 2.0 (the
				705	! "License"); you may not use this file except in compliance
				706	! with the License. You may obtain a copy of the License at
				707	!
				708	! http://www.apache.org/licenses/LICENSE-2.0
				709	!
				710	! Unless required by applicable law or agreed to in writing,
				711	! software distributed under the License is distributed on an
				712	! "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
				713	! KIND, either express or implied. See the License for the
				714	! specific language governing permissions and limitations
				715	! under the License.
				716	!-->
				717	</div></div>
				718	<div class="section">
				719	<h2><a name="Derived_Types"></a><a name="DerivedTypes" id="DerivedTypes">Derived Types</a></h2>
				720	<div class="section">
				721	<h3><a name="Object"></a><a name="DerivedTypesObject" id="DerivedTypesObject">Object</a></h3>
				722	<p>An <tt>object</tt> contains a set of ﬁelds, where each ﬁeld is described by its name and type. An object type may be defined as either open or closed. Open objects (instances of open object types) are permitted to contain ﬁelds that are not part of the type deﬁnition, while closed objects do not permit their instances to carry extra fields. An example type definition for an object is:</p>
				723
				724	<div>
				725	<div>
				726	<pre class="source"> create type SoldierType as open {
				727	name: string?,
				728	rank: string,
				729	serialno: int
				730	};
				731	</pre></div></div>
				732
				733	<p>Syntactically, object constructors are surrounded by curly braces “{…}”. Some examples of legitimate instances of the above type include:</p>
				734
				735	<div>
				736	<div>
				737	<pre class="source"> { "name": "Joe Blow", "rank": "Sergeant", "serialno": 1234567 }
				738	{ "rank": "Private", "serialno": 9876543 }
				739	{ "name": "Sally Forth", "rank": "Major", "serialno": 2345678, "gender": "F" }
				740	</pre></div></div>
				741
				742	<p>The first instance has all of the type’s prescribed content. The second instance is missing the name field, which is fine because it is optional (due to the ?). The third instance has an extra field; that is fine because the type definition specifies that it is open (which is also true by default, if open is not specified). To more tightly control object content, specifying closed instead of open in the type definition for SoldierType would have made the third example instance an invalid instance of the type.</p></div>
				743	<div class="section">
				744	<h3><a name="Array"></a><a name="DerivedTypesArray" id="DerivedTypesArray">Array</a></h3>
				745	<p>An <tt>array</tt> is a container that holds a fixed number of values. Array constructors are denoted by brackets: “[…]”.</p>
				746	<p>An example would be</p>
				747
				748	<div>
				749	<div>
				750	<pre class="source"> ["alice", 123, "bob", null]
				751	</pre></div></div>
				752	</div>
				753	<div class="section">
				754	<h3><a name="Multiset"></a><a name="DerivedTypesMultiset" id="DerivedTypesMultiset">Multiset</a></h3>
				755	<p>A <tt>multiset</tt> is a generalization of the concept of a set that, unlike a set, allows multiple instances of the multiset’s elements. Multiset constructors are denoted by two opening curly braces followed by data and two closing curly braces, like “{{…}}”.</p>
				756	<p>An example would be</p>
				757
				758	<div>
				759	<div>
				760	<pre class="source"> {{"hello", 9328, "world", [1, 2, null]}}
				761	</pre></div></div></div></div>
				762	</div>
				763	</div>
				764	</div>
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