Github user geomacy commented on a diff in the pull request:
https://github.com/apache/brooklyn-docs/pull/198#discussion_r124223906
--- Diff: guide/blueprints/catalog/versioning.md ---
@@ -3,18 +3,130 @@ title: Versioning
layout: website-normal
---
-### Versioning
+Brooklyn supports multiple versions of a type to be installed and used at
the same time.
+Versions are a first-class concept and are often prominently displayed in
the UI.
-Version numbers follow the OSGi convention. This can have a major, minor,
micro and qualifier part.
-For example, `1.0`. `1.0.1` or `1.0.1-20150101`.
+In order to do this, Brooklyn requires that the `id:version` string be
unique across the catalog:
+it is normally an error to add a type if a type with the same `id:version`
is present.
+The exceptions to this are if the definition is identical, or if the
`version` is noted as a `SNAPSHOT`.
+In extraordinary circumstances it may be appropriate to delete a given
`id:version` definition
+and then add the new one, but this is discouraged and the usual practice
is to:
-The combination of `id:version` strings must be unique across the catalog.
-It is an error to deploy the same version of an existing item:
-to update a blueprint, it is recommended to increase its version number;
-alternatively in some cases it is permitted to delete an `id:version`
instance
-and then re-deploy.
-If no version is specified, re-deploying will automatically
-increment an internal version number for the catalog item.
+* Use a `-SNAPSHOT` qualifer suffix on your version when developing
+* Increase the version number when making a change to a non-SNAPSHOT type
+
+When adding to the catalog, if no version is supplied, Brooklyn may
automatically
+increment the version number for the catalog item.
+
+When deploying a blueprint, if a version number is not specified Brooklyn
will typically use
+the highest ordered version (see "Ordering" below) in the catalog for the
referenced type,
+and will thereafter lock the use of that version in that blueprint.
+(An exception is where types are co-bundled or an explicit search path is
defined;
+in the context of evaluating one type, Brooklyn may prefer versions in the
same bundle or on the search path.)
+
+
+#### Versioning Syntax
+
+Version numbers in Brooklyn are recommended to follow the following syntax:
+
+```
+<major> ( "." <minor> ( "." <patch> )? )? ( "-" <qualifier> )?
+```
+
+where the `<major>`, `<minor>`, and `<patch>` parts are numbers
+in accordance with [semver](http://semver.org) semantic versioning,
+assumed to be `0` if omitted,
+and an `<qualifier>` is made up of letters, numbers, `"-"` and `"_"`
+in accordance with
[OSGi](https://www.osgi.org/release-4-version-4-3-download/)
+(see sections 1.3.2 and 3.2.5).
+
+Examples:
+
+* `1.2`
+* `2.0.0`
+* `3`
+* `2.0.0-SNAPSHOT`
+* `1.10-rc3-20170619`
+
+
+#### Snapshots and Ordering
+
+The string `SNAPSHOT` appearing anywhere in the version indicates a
pre-release version;
+if this string is not present the version is treated as a release version.
+
+When taking an ordering, for instance to find the highest version,
+snapshot versions are always considered lower than release versions.
+Next, the natural order is taken on the major, minor, and patch fields.
+Next, a version with no qualifier is considered higher than one with a
qualifier.
+Finally, the qualifier is taken in natural order.
+
+The natural order here is defined as ASCII-lexicographic comparison
+for any non-numeric segments (`"a" < "b"`) but numeric order for digit
sequences
+(`"9" < "10"`), so it does what is usually expected for versions (`1.9` <
`1.10`
+and `"1.1-rc9-b" < "1.1-rc10-a"`).
--- End diff --
This actually puts us at odds with OSGI - they define _qualifier_
comparison to be simply lexicographic. For OSGI, `1.1.0.rc9-b > 1.1.0.rc10-a`.
If we are converting versions to bundle versions internally we need to match
the OSGI version comparison rules. E.g. when brooklyn is working out what the
latest version of a bundle is, we don't want Brooklyn choosing a different
version than OSGI thinks is the latest.
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