[midPoint] XML attributes
Deepak Natarajan
dnataraj at trilobytesystems.com
Thu Jul 3 18:40:50 CEST 2014
Hi Radovan -
I would like to return to this issue we discussed earlier.
You mentioned :
"When it comes to your specific case I'm sure that the data can be
represented in an alternative way without the use of attributes. Of
course you can use this:
<group>
<id>1</id>
<value>a</value>
</group>
<group>
<id>2</id>
<value>b</value>
</group> "
I would like to use this, but am wondering how the inbound mappings
would be set up in order to set <id> and <value> in separate mappings.
(and they should be for the same <group> instance)
In our use case, we have different group "types". What this boils down
to is that these groups belong in different OU's (i.e group Foo with
type A is under ou=A,o=root,.. and group boo with Type B has a dn
cn=Boo, ou=B, o=root etc.) - And more types can arise in the future.
In your org sync example, you kept it simple and added all the groups
under on OU. I took this a bit further and examine the group name for
clues as to where it belongs (it was obvious at one point - but our
customer has introduced some new ideas *sigh*)
I am trying to build an elegant, flexible solution for this. To somehow
propagate these "group types" to my Midpoint User (who has a sequence of
<group>'s), onto my Roles and then finally use this to provision the
groups correctly in the various OU's.
I started off by trying to have a better extension schema :
<groups>
<group>
<name>foo</name>
<type>A</type>
<group>
...
...
</groups>
I'm not sure if this is possible (I have read your detailed input on XML
usage within Midpoint) and how I would do inbound mapping for such
extension elements (considering that my source feed can provide group
name and type)
And then I would have to deal with role mappings in the user template in
order to propagate this as an extension atttribute of Role, and then use
this value to figure out the base dn for the group (I have installed my
static custom class in Midpoint that returns this value). The idea is to
be able to inject new group types at runtime.
Essentially I'm looking for a pattern to solve the general case of
mapping our source systems rich attributes onto various extended
attributes for key Midpoint focal objects such as User & Group.
A use case for us is that when a department has a new attribute in the
source system (e.g this department is only for "managers"), we need this
to translate to a group that is under a specific OU (and this is
independent of org sync - i.e users assigned to orgs).
I've dumped a lot here, but any thoughts? :)
As always, thanks in advance.
BR/Deepak
> Radovan Semancik <mailto:radovan.semancik at evolveum.com>
> May 28, 2014 at 7:54 PM
> Hi Deepak,
>
> I guess I have a bad news for you. But this is quite a long story, so
> let's start at the beginning.
>
> When we have designed midPoint a couple of years ago we have built it
> quite tightly on top of XML. That was still the obvious choice at that
> time and also some kind of a best practice. And it was not a bad
> choice. Especially considering that alternatives such as JSON were
> still it their infancy ... and actually they haven't evolved a bit in
> all these years - but that's a different story. So, we have built
> midPoint on top of XML.
>
> But the XML stroke back. I was not naive and I was aware that XML is
> not perfect when we started with midPoint. But I somehow expected that
> we can live with it at least for few years. I was wrong. XML and XSD
> and WSDL are terribly bad at handling dynamic schemas. I mean schemas
> that are only available at runtime. MidPoint schema extension is one
> example of such schema. But there are many more examples: resource
> schema, connector schema, reports, ...
>
> Most other IDM system obviously deal with this problem by ignoring it.
> They do not support schema at all. But this was not the path that we
> wanted to take with midPoint. MidPoint is fully schema-based from the
> bottom (connectors) to the top (GUI). And there are huge advantages to
> this architecture. But there are also challenges. And dealing with XSD
> and especially Sun XML libraries was a huge challenge.
>
> And that was the origin of "Prism Objects". We started to slowly
> replace XML libraries with a more generic data representation layer. See:
> https://wiki.evolveum.com/display/midPoint/Prism+Objects
>
> That was approximately the time when JSON became more popular than
> XML. And midPoint users started to ask about JSON support. I
> personally do not like JSON way of doing things. But we need to listen
> to user requests. And we have realized that we can easily support JSON
> and also other languages with our Prism layer. And I actually see an
> advantage in using readable languages such as YAML. Therefore we have
> chosen to go for language independence. XML is just one of possible
> data representation languages now. JSON and YAML will be available soon.
>
> Currently midPoint (v3.0) is almost completely based on Prism. It is
> not using the XML layer directly perhaps except for several places
> that we plan to rewrite in next releases. This gives us the ability to
> represent data theoretically in any reasonable format. XML is the
> primary one. But it is not the only one.
>
> And now it gets to the point of XML attributes. XML is a very strange
> format for data representation. It has nice features (such as safe
> extensibility with namespaces) and it has really bad features.
> Attributes are one of the worse features. Non-structured data item can
> be represented both as an attribute and as an sub-element. This
> creates a dichotomy that puzzled software engineers almost since XML
> was created. And it is a deadly trap for language-neutral data
> abstractions such as our Prism. Also languages such as JSON do not
> have attributes at all. And even though we try to have complete schema
> for everything there are some corner cases when we need to work
> without a schema. And then there may be problem whether to represent
> JSON key as XML attribute or sub-element.
>
> Therefore we have decided to slowly phase out the support for XML
> attributes. MidPoint version 3.0 interprets attributes in the same way
> as sub-elements. And in fact these are interchangeable at many places
> in midPoint XML structures. And more places will appear in next
> versions. This is the plan for the entire 3.x generation. The 4.x
> versions will probably not use attributes at all.
>
> So, the use of attributes is still somehow supported. But not
> recommended. And the way how you try to use the attributes as a map
> will not work in midPoint 3.x. It is not compatible with our data
> representation.
>
> When it comes to your specific case I'm sure that the data can be
> represented in an alternative way without the use of attributes. Of
> course you can use this:
> <group>
> <id>1</id>
> <value>a</value>
> </group>
> <group>
> <id>2</id>
> <value>b</value>
> </group>
>
> And there is another catch. As we are moving away from XML we also
> have to move away from XML-dependent mechanisms. Such as XPath.
> Therefore XPath has limited capabilities in midPoint 3.x. In fact if
> you define a schema then midPoint will not think about the data in XML
> terms. It will not see XML elements any more. It does not see the
> document, it sees the data. It will see the data structure as
> multi-value structured property "group". XPath may not be applicable
> here.
>
> Therefore I guess this is still not the best way to represent your
> data. Maybe I could help you design the data structure if you describe
> the way how you plan to use the group data from the user object.
>
> Deepak Natarajan <mailto:dnataraj at trilobytesystems.com>
> May 26, 2014 at 1:32 PM
> Hi everyone -
>
> I am trying to achieve the following inbound mapping :
>
> from resource :
> "groups" : "a_1,b_2,c_3,d_4"
>
> to
>
> <user>
> <group id="1">a</group>
> <group id="2">b</group>
> <group id="3">c</group>
> </user>
>
> My custom schema extension seems to be accepted by Midpoint. I have
> extended the UserType to support a multi-valued child element <group>
> with an "id" attribute (I have a GroupType defined in my custom schema).
>
> I can achieve the simple case, without the "id" attribute. So I can see
> in the Admin Console that the User has several groups, which I do with
> the following mapping :
>
> <attribute>
> <ref>ri:groups</ref>
> <inbound>
> <expression>
> <script>
> <code>
> [parse input and return array of string [a, b,
> c...]
> </code>
> </script>
> </expression>
> <target>
> <path>$user/extension/my:group</path>
> </target>
> </inbound>
> </attribute>
>
> Now I'm trying to map attributes for the group element
> ($user/extension/my:group/@id)
>
> Has anyone tried this? Thanks for any input!
>
> BR/
--
Deepak Natarajan
Director
Trilobyte Systems ApS
Falkoner Alle 1, 3 Frederikinkatu 61A, 6th Floor
2000 Frederiksberg Business Center Papula
Denmark 00100 Helsinki
Finland
Tel : +45 29375068
http://www.trilobytesystems.com
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