Update naming guidance for id properties, transitiveChildren properties, and completedDateTime common property name (#507)

Author: corranrogue9

graph/GuidelinesGraph.md

@@ -104,6 +104,7 @@ Following is a short summary of the most often used conventions.
 | **CASING** | |
 | :heavy_check_mark: **MUST** use lower camel case for *all* names and namespaces.   | - **Right:** automaticRepliesStatus <BR> - **Wrong:** kebab-case or snake_case |
 | :ballot_box_with_check: **SHOULD** case two-letter acronyms with the same case.   | - **Right:** ioLimit or totalIOAmount <BR> - **Right:** 'id' properties similar to driveId or applicationId <BR> - **Wrong:** iOLimit or totalIoAmount|
+| :ballot_box_with_check: **SHOULD** case `id` properties the same as a normal word.   | - **Right:** id or fileId <BR> - **Wrong:** ID or fileID |
 | :ballot_box_with_check: **SHOULD** case three+ letter acronyms the same as a normal word.  | - **Right:** fidoKey or oauthUrl <BR> - **Wrong:** webHTML |
 | :no_entry: **MUST NOT** capitalize the word following a [prefix](https://www.thoughtco.com/common-prefixes-in-english-1692724) or words within a [compound word](http://www.learningdifferences.com/Main%20Page/Topics/Compound%20Word%20Lists/Compound_Word_%20Lists_complete.htm).                                     | - **Right:** subcategory, geo coordinate, or crosswalk <BR> - **Wrong:** metaData, semiCircle, or airPlane |
 | :heavy_check_mark: **MUST** capitalize within hyphenated and open (spaced) compound words. | - **Right:** fiveYearOld, daughterInLaw, or postOffice <BR> - **Wrong:** paperclip or fullmoon |
@@ -116,6 +117,13 @@ Following is a short summary of the most often used conventions.
 | :no_entry: **MUST NOT** use collection, response, or request suffixes.  | - **Right:** addresses <BR> - **Wrong:** addressCollection |
 | :no_entry: **MUST NOT** contain  product names.  | - **Right:** chatMessages <BR> - **Wrong:** teamsMessages |
 
+#### Tree and graph structures
+
+When a tree or graph structure is being modeled, the direct sub-nodes are usually named `children` or `members`. 
+If a property is desired that represents a "flattened" data structure, the property **SHOULD** be prefixed with "transitive", e.g. `transitiveChildren` or `transitiveMembers`.
+Such properties **MUST** represent a mathematically [transitive relationship](https://en.wikipedia.org/wiki/Transitive_relation). 
+To simplify, if `A` is a child of `B` and `B` is a child of `C`, then `A` is a child of `C` via a transitive relationship; this **MUST** be true for properties using word "transitive" in their name.
+
 ### Uniform Resource Locators (URLs)
 
 A Uniform Resource Locator (URL) is how developers access the resources of your API.

graph/articles/naming.md

@@ -60,39 +60,40 @@ Where services have a property, whose data matches the names below, the service
 This table will grow as services add terms that will be more commonly used.
 Service owners adding such terms SHOULD propose additions to this document.
 
-| |
-|------------- |
- attendees     |
- body          |
- createdDateTime |
- childCount    |
- children      |
- contentUrl    |
- country       |
- createdBy     |
- displayName   |
- errorUrl      |
- eTag          |
- event         |
- expirationDateTime |
- givenName     |
- jobTitle      |
- kind          |
- id            |
+|                     |   |
+|-------------------- | - |
+ attendees            |
+ body                 |
+ completedDateTime    | **NOTE** completionDateTime may be used for cases where the timestamp represents a point in the future |
+ createdDateTime      |
+ childCount           |
+ children             |
+ contentUrl           |
+ country              |
+ createdBy            |
+ displayName          |
+ errorUrl             |
+ eTag                 |
+ event                |
+ expirationDateTime   |
+ givenName            |
+ jobTitle             |
+ kind                 |
+ id                   |
  lastModifiedDateTime |
- location      |
- memberOf      |
- message       |
- name          |
- owner         |
- people        |
- person        |
- postalCode    |
- photo         |
- preferredLanguage |
- properties    |
- signInName    |
- surname       |
- tags          |
- userPrincipalName |
- webUrl        |
+ location             |
+ memberOf             |
+ message              |
+ name                 |
+ owner                |
+ people               |
+ person               |
+ postalCode           |
+ photo                |
+ preferredLanguage    |
+ properties           |
+ signInName           |
+ surname              |
+ tags                 |
+ userPrincipalName    |
+ webUrl               |