Module Documentation: eml-access
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The eml-access module - Access control rules for resources

The eml-access module describes the level of access that is to be allowed or denied to a resource for a particular user or group of users, and can be described independently for metadata and data. The eml-access module uses a reference to a particular authentication system to determine the set of principals (users or groups) that can be specified in the access rules. The special principal 'public' can be used to indicate that any user or group has access permission, thereby making it easier to specify that anonymous access is allowed.

There are two mechanisms for including access control via the eml-access module:

The top-level "eml" element may have an optional <access> element that is used to establish the default access control for the entire EML package. If this access element is omitted from the document, then the package submitter should be given full access to the package but all other users should be denied all access. To allow the package to be publicly viewable, the EML author must explicitly include a rule stating so. Barring the existence of a distribution-level <access> element (see below), access to data entities will be controlled by the package-level <access> element in the <eml> element.

Exceptions for particular entity-level components of the package can be controlled at a finer grain by using an access description in that entity's physical/distribution tree. When access control rules are specified at this level, they apply only to the data in the parent distribution element, and not to the metadata. Thus, it will control access to the content of the <inline> element, as well as resources that are referenced by the <online/url> and <online/connection> paths. These exceptions to access for particular data resources are applied after the default access rules at the package-level have been applied, so they effectively override the default rules when they overlap.

In previous versions of EML access rules for entity-level distribution were contained in <additionalMetadata> sections and referenced via the <describes> tag. Although in theory these could have referenced any node, in application such node-level access control is problematic. Since the most common uses of access control rules were to limit access to specific data entities, the access tree has been placed there explicitly in EML 2.1.0.

Access is specified with a choice of child elements, either <allow> or <deny>. Within these rules, values can be assigned for each <principal> using the <permission> element. Users given "read" permission can view the resource; "write" allows changes to the resource excluding changes to the access rules; "changePermission" includes "write" plus the changing of access rules. Users allowed "all" permissions; may do all of the above. Access to data and metadata is affected by the order attribute of the <access> element. It is possible for a deny rule to override an allow rule, and vice versa. In the case where the order attribute is set to "allowFirst", and there are rules similar to the following (with non-critical sections deleted): 

  <deny>
    <principal>public</principal>
    <permission>read</permission>
  </deny>
  <allow>
    <principal>uid=alice,o=NASA,dc=ecoinformatics,dc=org</principal>
    <permission>read</permission>
  </allow>
the principal "uid=alice ..." will be denied access, because it is a member of the special "public" principal, and the deny rule is processed second. For this allow rule to truly allow access to that principal, the order attribute should be set to "denyFirst", and the allow rule will override the deny rule when it is processed second.

An example is given below, with non-critical sections deleted: 

  <eml>
      <access 
          authSystem="ldap://ldap.ecoinformatics.org:389/dc=ecoinformatics,dc=org" 
          order="allowFirst">
        <allow>
          <principal>uid=alice,o=NASA,dc=ecoinformatics,dc=org</principal>
          <permission>read</permission>
          <permission>write</permission>
        <allow>
      </access>
      <dataset>
      ...
      ...
      <dataTable id="entity123">
      ...
        <physical>
        ...
          <distribution>
          ...
            <access id="access123"
            authSystem="ldap://ldap.ecoinformatics.org:389/dc=ecoinformatics,dc=org" 
            order="allowFirst">
              <deny>
                <principal>uid=alice,o=NASA,dc=ecoinformatics,dc=org</principal>
                <permission>write</permission>
            </deny>
          </access>
         </distribution>
       </physical>
      </dataTable>
      <dataTable id="entity234">
        ...
        <physical>
        ...
          <distribution>
            ...
            <access>
              <references>access123</references>
            </access>
          </distribution>
        </physical>
      </dataTable>
      ...    
    </dataset>
  <eml>
In this example, the overall default access is to allow the user=alice (but no one else) to read and write all metadata and data. However, under "entity123" and "entity234", there is an additional rule saying that user=alice does not have write permission. The net effect is that Alice can read and make changes to the metadata, but cannot make changes to the two data entities. In addition, Alice cannot change these access rules; although the submitter can.

This example also shows how the eml-access module, like other modules, may be "referenced" via the <references> tag. This allows an access control document to be described once, and then used as a reference in other locations within the EML document via its ID.

In summary, access rules can be applied in two places in an eml document. Default access rules are established in the top <access> element for the main eml document (e.g., "/eml/access"). These default rules can be overridden for particular data entities by adding additional <access> elements in the physical/distribution trees of those entities.

Module details
Recommended Usage: all data where controlling user access to the dataset is an issue
Stand-alone: yes
Imports: eml-documentation, eml-resource
Imported By:
View an image of the schema: eml-access image

Element Definitions:
access  This element has no default value.
Content of this field: Description of this field:
Type: AccessType
The access element contains a list of rules defining permissions for this resource. For descriptions of the individual elements, see the AccessType.The permission rules defined here can be overridden by rules added to an access tree in the PhysicalDistributionType at the entity level.
Example(s):
See the description of the AccessType.
allow  This element has no default value.
Content of this field: Description of this field:
Type: AccessRule
The allow element indicates that a particular user or group is granted the defined permission.
Example(s):
allow
deny  This element has no default value.
Content of this field: Description of this field:
Type: AccessRule
The deny element indicates that a particular user or group is not granted the defined permission.
Example(s):
deny
principal  This element has no default value.
Content of this field: Description of this field:
Type: res:NonEmptyStringType
The principal element defines the user or group to which the access control rule applies. The users and groups must be defined in the authentication system described in the authSystem element. The special principal 'public' can be used to indicate that any user or group has a particular access permission, thereby making it easier to specify that anonymous access is allowed.
Example(s):
public
uid=alice,o=LTER,dc=ecoinformatics,dc=org
permission  This element has no default value.
Content of this field: Description of this field:

The permission that is being granted or denied to a particular user or group for a given resource. The list of permissions come from a predetermined list:

'read' - allow or deny viewing of the resource,

'write' - allow or deny modification of the resource (except for access rules),

'changePermission' - modifications including access rules, and

'all' - all of the above.

This element also allows other permission values that may be applicable to some other authentication systems but are not defined in this specification (if these other values are used, access rule enforcement is indeterminate outside of the originating system).


Example(s):
read

Attribute Definitions:
id

Type: res:IDType

Use: optional

system

Type: res:SystemType

Use: optional

scope

Type: res:ScopeType

Use: optional

Default value: document

order

Use: optional

Default value: allowFirst

Derived from: xs:string (by xs:restriction)

Allowed values:

  • allowFirst
  • denyFirst
To obtain the desired access control, use the order attribute to define which rules should be applied first. The acceptable values are 'allowFirst' and 'denyFirst'. If 'allowFirst' is specified, then all 'allow' rules are processed, and then overridden by all 'deny' rules. If 'denyFirst' is specified, then all 'deny' rules are processed, and then overridden by all 'allow' rules.
Example(s):
allowFirst
authSystem

Type: xs:string

Use: required

The authentication system determines the set of principals (users + groups) that can be used in the access control list, and the membership of users in groups. This element is intended to provide a reference to the authentication system that is used to verify the user or group. This reference is typically in the form of a URI, which includes the connection protocol, Internet host, and path to the authentication mechanism.
Example(s):
ldap://ldap.ecoinformatics.org:389/dc=ecoinformatics,dc=org

Complex Type Definitions:
AccessType 
Content of this field: Description of this field:
Elements: Use: How many:
A choice of (
A choice of (
allowrequired
OR
denyrequired
)
res:ReferencesGroup  
)
Attributes: Use: Default Value:
idoptional
systemoptional
scopeoptionaldocument
orderoptionalallowFirst
authSystemrequired
The access element contains a list of rules that define the level of access for a resource. There are two uses of access trees: to control access to either metadata or data. To control access to metadata use the eml/access tree. By default, these rules will also apply to the contained data. To override the default controls for specific data entities, use the access element available in the entity's physical/distribution tree. A combination of access trees and their "order rules" (see description of the "order" attribute) allows EML authors to have fine control over permissions for individuals and groups.
AccessRule 
Content of this field: Description of this field:
Elements: Use: How many:
A sequence of (
principalrequiredunbounded
permissionrequiredunbounded
)
The AccessRule type defines a list of users that are derived from a particular authentication system (such as an LDAP directory), whether the user or group is allowed or denied access, the extent of their access (read, write , or changePermission access).

Simple Type Definitions:

Group Definitions:

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