Added some info about open and close types to the data model doc.
Change-Id: I1262090a2a568d935fd96e00db1da5cd836f25a5
Reviewed-on: https://asterix-gerrit.ics.uci.edu/1510
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Yingyi Bu <buyingyi@gmail.com>
diff --git a/asterixdb/asterix-doc/src/site/markdown/datamodel.md b/asterixdb/asterix-doc/src/site/markdown/datamodel.md
index cba0d18..2c8a015 100644
--- a/asterixdb/asterix-doc/src/site/markdown/datamodel.md
+++ b/asterixdb/asterix-doc/src/site/markdown/datamodel.md
@@ -350,7 +350,7 @@
### <a id="IncompleteInformationTypesMissing">Missing</a> ###
-`missing` represents a missing name-value pair in a object.
+`missing` represents a missing name-value pair in an object.
If the referenced field does not exist, an empty result value is returned by the query.
As neither the data model nor the system enforces homogeneity for datasets or collections,
@@ -371,13 +371,22 @@
## <a id="DerivedTypes">Derived Types</a> ##
### <a id="DerivedTypesObject">Object</a>###
-A `object` contains a set of fields, where each field is described by its name and type. A object type is either open or closed. Open objects can contain fields that are not part of the type definition, while closed objects cannot. Syntactically, object constructors are surrounded by curly braces "{...}".
+An `object` 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:
-An example would be
+ create type SoldierType as open {
+ name: string?,
+ rank: string,
+ serialno: int
+ };
+Syntactically, object constructors are surrounded by curly braces "{...}".
+Some examples of legitimate instances of the above type include:
- { "id": 213508, "name": "Alice Bob" }
+ { "name": "Joe Blow", "rank": "Sergeant", "serialno": 1234567 }
+ { "rank": "Private", "serialno": 9876543 }
+ { "name": "Sally Forth", "rank": "Major", "serialno": 2345678, "gender": "F" }
+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.
### <a id="DerivedTypesArray">Array</a>###
An `array` is a container that holds a fixed number of values. Array constructors are denoted by brackets: "[...]".