openldap/doc/guide/admin/schema.sdf

# $OpenLDAP$
# Copyright 1999-2020 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.

H1: Schema Specification

This chapter describes how to extend the user schema used by
{{slapd}}(8).  The chapter assumes the reader is familiar with the
{{TERM:LDAP}}/{{TERM:X.500}} information model.

The first section, {{SECT:Distributed Schema Files}} details optional
schema definitions provided in the distribution and where to obtain
other definitions.
The second section, {{SECT:Extending Schema}}, details how to define
new schema items.
!if 0
The third section, {{SECT:Transferring Schema}} details how you can
export schema definitions from an LDAPv3 server and transform it
to {{slapd.conf}}(5) format.
!endif

This chapter does not discuss how to extend system schema used by
{{slapd}}(8) as this requires source code modification.  System
schema includes all operational attribute types or any object class
which allows or requires an operational attribute (directly or
indirectly).


H2: Distributed Schema Files

OpenLDAP Software is distributed with a set of schema specifications for
your use.  Each set is defined in a file suitable for inclusion
(using the {{EX:include}} directive) in your {{slapd.conf}}(5)
file.  These schema files are normally installed in the
{{F:/usr/local/etc/openldap/schema}} directory.

!block table; colaligns="LR"; coltags="F,N"; align=Center; \
	title="Table 8.1: Provided Schema Specifications"
File			Description
core.schema		OpenLDAP {{core}} (required)
cosine.schema		Cosine and Internet X.500 (useful)
inetorgperson.schema	InetOrgPerson (useful)
misc.schema		Assorted (experimental)
nis.schema		Network Information Services (FYI)
openldap.schema		OpenLDAP Project (experimental)
!endblock

To use any of these schema files, you only need to include the
desired file in the global definitions portion of your
{{slapd.conf}}(5) file.  For example:

>	# include schema
>	include /usr/local/etc/openldap/schema/core.schema
>	include /usr/local/etc/openldap/schema/cosine.schema
>	include /usr/local/etc/openldap/schema/inetorgperson.schema

Additional files may be available.  Please consult the OpenLDAP
{{TERM:FAQ}} ({{URL:http://www.openldap.org/faq/}}).

Note: You should not modify any of the schema items defined
in provided files.


H2: Extending Schema

Schema used by {{slapd}}(8) may be extended to support additional
syntaxes, matching rules, attribute types, and object classes.  This
chapter details how to add user application attribute types and
object classes using the syntaxes and matching rules already supported
by slapd.  slapd can also be extended to support additional syntaxes,
matching rules and system schema, but this requires some programming
and hence is not discussed here.

There are five steps to defining new schema:
^	obtain Object Identifier
+	choose a name prefix
+	create local schema file
+	define custom attribute types (if necessary)
+	define custom object classes


H3: Object Identifiers

Each schema element is identified by a globally unique {{TERM[expand]OID}}
(OID).  OIDs are also used to identify other objects.  They are
commonly found in protocols described by {{TERM:ASN.1}}.  In
particular, they are heavily used by the {{TERM[expand]SNMP}} (SNMP).
As OIDs are hierarchical, your organization can obtain one OID and
branch it as needed.  For example, if your organization were assigned
OID {{EX:1.1}}, you could branch the tree as follows:

!block table; colaligns="LR"; coltags="EX,N"; align=Center; \
	title="Table 8.2: Example OID hierarchy"
OID		Assignment
1.1		Organization's OID
1.1.1		SNMP Elements
1.1.2		LDAP Elements
1.1.2.1		AttributeTypes
1.1.2.1.1	x-my-Attribute
1.1.2.2		ObjectClasses
1.1.2.2.1	x-my-ObjectClass
!endblock

You are, of course, free to design a hierarchy suitable to your
organizational needs under your organization's OID. No matter what hierarchy you choose, you should maintain a registry of assignments you make.  This can be a simple flat file or something more sophisticated such as the {{OpenLDAP OID Registry}} ({{URL:http://www.openldap.org/faq/index.cgi?file=197}}).

For more information about Object Identifiers (and a listing service)
see {{URL:http://www.alvestrand.no/objectid/}}.

.{{Under no circumstances should you hijack OID namespace!}}

To obtain a registered OID at {{no cost}}, apply for a OID
under the {{ORG[expand]IANA}} (ORG:IANA) maintained {{Private Enterprise}} arc.  
Any private enterprise (organization) may request a {{TERM[expand]PEN}} (PEN) to be assigned under this arc. Just fill out the IANA form at {{URL: http://pen.iana.org/pen/PenApplication.page}} and your official PEN will be sent to you usually within a few days. Your base OID will be something like {{EX:1.3.6.1.4.1.X}} where {{EX:X}} is an integer.

Note: PENs obtained using this form may be used for any purpose
including identifying LDAP schema elements.

Alternatively, OID name space may be available from a national
authority (e.g., {{ORG:ANSI}}, {{ORG:BSI}}).


H3: Naming Elements

In addition to assigning a unique object identifier to each schema
element, you should provide at least one textual name for each
element.  Names should be registered with the {{ORG:IANA}} or
prefixed with "x-" to place in the "private use" name space.

The name should be both descriptive and not likely to clash with
names of other schema elements.  In particular, any name you choose
should not clash with present or future Standard Track names (this
is assured if you registered names or use names beginning with "x-").

It is noted that you can obtain your own registered name
prefix so as to avoid having to register your names individually.
See {{REF:RFC4520}} for details.

In the examples below, we have used a short prefix '{{EX:x-my-}}'.
Such a short prefix would only be suitable for a very large, global
organization.  In general, we recommend something like '{{EX:x-de-Firm-}}'
(German company) or '{{EX:x-com-Example}}' (elements associated with
organization associated with {{EX:example.com}}).


H3: Local schema file

The {{EX:objectclass}} and {{EX:attributeTypes}} configuration file
directives can be used to define schema rules on entries in the
directory.  It is customary to create a file to contain definitions
of your custom schema items.  We recommend you create a file
{{F:local.schema}} in {{F:/usr/local/etc/openldap/schema/local.schema}}
and then include this file in your {{slapd.conf}}(5) file immediately
after other schema {{EX:include}} directives.

>	# include schema
>	include /usr/local/etc/openldap/schema/core.schema
>	include /usr/local/etc/openldap/schema/cosine.schema
>	include /usr/local/etc/openldap/schema/inetorgperson.schema
>	# include local schema
>	include /usr/local/etc/openldap/schema/local.schema


H3: Attribute Type Specification

The {{attributetype}} directive is used to define a new attribute
type.  The directive uses the same Attribute Type Description
(as defined in {{REF:RFC4512}}) used by the attributeTypes
attribute found in the subschema subentry, e.g.:

E:	attributetype <{{REF:RFC4512}} Attribute Type Description>

where Attribute Type Description is defined by the following
{{TERM:ABNF}}:

>      AttributeTypeDescription = "(" whsp
>            numericoid whsp              ; AttributeType identifier
>          [ "NAME" qdescrs ]             ; name used in AttributeType
>          [ "DESC" qdstring ]            ; description
>          [ "OBSOLETE" whsp ]
>          [ "SUP" woid ]                 ; derived from this other
>                                         ; AttributeType
>          [ "EQUALITY" woid              ; Matching Rule name
>          [ "ORDERING" woid              ; Matching Rule name
>          [ "SUBSTR" woid ]              ; Matching Rule name
>          [ "SYNTAX" whsp noidlen whsp ] ; Syntax OID
>          [ "SINGLE-VALUE" whsp ]        ; default multi-valued
>          [ "COLLECTIVE" whsp ]          ; default not collective
>          [ "NO-USER-MODIFICATION" whsp ]; default user modifiable
>          [ "USAGE" whsp AttributeUsage ]; default userApplications
>          whsp ")"
>
>      AttributeUsage =
>          "userApplications"     /
>          "directoryOperation"   /
>          "distributedOperation" / ; DSA-shared
>          "dSAOperation"          ; DSA-specific, value depends on server
>

where whsp is a space ('{{EX: }}'), numericoid is a globally unique
OID in dotted-decimal form (e.g. {{EX:1.1.0}}), qdescrs is one or
more names, woid is either the name or OID optionally followed
by a length specifier (e.g {{EX:{10}}}).

For example, the attribute types {{EX:name}} and {{EX:cn}} are defined
in {{F:core.schema}} as:

>	attributeType ( 2.5.4.41 NAME 'name'
>		DESC 'name(s) associated with the object'
>		EQUALITY caseIgnoreMatch
>		SUBSTR caseIgnoreSubstringsMatch
>		SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{32768} )
>	attributeType ( 2.5.4.3 NAME ( 'cn' 'commonName' )
>		DESC 'common name(s) associated with the object'
>		SUP name )

Notice that each defines the attribute's OID, provides a short name,
and a brief description.  Each name is an alias for the OID.
{{slapd}}(8) returns the first listed name when returning results.

The first attribute, {{EX:name}}, holds values of {{EX:directoryString}}
({{TERM:UTF-8}} encoded Unicode) syntax.  The syntax is
specified by OID (1.3.6.1.4.1.1466.115.121.1.15 identifies the
directoryString syntax).  A length recommendation of 32768 is
specified.  Servers should support values of this length, but may
support longer values. The field does NOT specify a size constraint,
so is ignored on servers (such as slapd) which don't impose such
size limits.  In addition, the equality and substring matching uses
case ignore rules.  Below are tables listing commonly used syntax
and matching rules ({{slapd}}(8) supports these and many more).

!block table; align=Center; coltags="EX,EX,N"; \
	title="Table 8.3: Commonly Used Syntaxes"
Name			OID				Description
boolean			1.3.6.1.4.1.1466.115.121.1.7	boolean value
directoryString		1.3.6.1.4.1.1466.115.121.1.15	Unicode (UTF-8) string
distinguishedName	1.3.6.1.4.1.1466.115.121.1.12	LDAP {{TERM:DN}}
integer			1.3.6.1.4.1.1466.115.121.1.27	integer
numericString		1.3.6.1.4.1.1466.115.121.1.36	numeric string
OID			1.3.6.1.4.1.1466.115.121.1.38	object identifier
octetString		1.3.6.1.4.1.1466.115.121.1.40	arbitrary octets
!endblock

> 

!block table; align=Center; coltags="EX,N"; \
	title="Table 8.4: Commonly Used Matching Rules"
Name					Type		Description
booleanMatch				equality	boolean
caseIgnoreMatch				equality	case insensitive, space insensitive
caseIgnoreOrderingMatch			ordering	case insensitive, space insensitive
caseIgnoreSubstringsMatch		substrings	case insensitive, space insensitive
caseExactMatch				equality	case sensitive, space insensitive
caseExactOrderingMatch			ordering	case sensitive, space insensitive
caseExactSubstringsMatch		substrings	case sensitive, space insensitive
distinguishedNameMatch			equality	distinguished name
integerMatch				equality	integer
integerOrderingMatch			ordering	integer
numericStringMatch			equality	numerical
numericStringOrderingMatch		ordering	numerical
numericStringSubstringsMatch		substrings	numerical
octetStringMatch			equality	octet string
octetStringOrderingMatch		ordering	octet string
octetStringSubstringsMatch	ordering	octet string
objectIdentiferMatch			equality	object identifier
!endblock

The second attribute, {{EX:cn}}, is a subtype of {{EX:name}} hence
it inherits the syntax, matching rules, and usage of {{EX:name}}.
{{EX:commonName}} is an alternative name.

Neither attribute is restricted to a single value.  Both are meant
for usage by user applications.  Neither is obsolete nor collective.

The following subsections provide a couple of examples.


H4: x-my-UniqueName

Many organizations maintain a single unique name for each user.
Though one could use {{EX:displayName}} ({{REF:RFC2798}}), this
attribute is really meant to be controlled by the user, not the
organization.  We could just copy the definition of {{EX:displayName}}
from {{F:inetorgperson.schema}} and replace the OID, name, and
description, e.g:

>	attributetype ( 1.1.2.1.1 NAME 'x-my-UniqueName'
>		DESC 'unique name with my organization' 
>		EQUALITY caseIgnoreMatch
>		SUBSTR caseIgnoreSubstringsMatch
>		SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
>		SINGLE-VALUE )

However, if we want this name to be used in {{EX:name}} assertions,
e.g. {{EX:(name=*Jane*)}}, the attribute could alternatively be
defined as a subtype of {{EX:name}}, e.g.:

>	attributetype ( 1.1.2.1.1 NAME 'x-my-UniqueName'
>		DESC 'unique name with my organization' 
>		SUP name )


H4: x-my-Photo

Many organizations maintain a photo of each each user.  A
{{EX:x-my-Photo}} attribute type could be defined to hold a photo.
Of course, one could use just use {{EX:jpegPhoto}} ({{REF:RFC2798}})
(or a subtype) to hold the photo.  However, you can only do
this if the photo is in {{JPEG File Interchange Format}}.
Alternatively, an attribute type which uses the {{Octet String}}
syntax can be defined, e.g.:

>	attributetype ( 1.1.2.1.2 NAME 'x-my-Photo'
>		DESC 'a photo (application defined format)' 
>		SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
>		SINGLE-VALUE )

In this case, the syntax doesn't specify the format of the photo.
It's assumed (maybe incorrectly) that all applications accessing
this attribute agree on the handling of values.

If you wanted to support multiple photo formats, you could define
a separate attribute type for each format, prefix the photo
with some typing information, or describe the value using
{{TERM:ASN.1}} and use the {{EX:;binary}} transfer option.

Another alternative is for the attribute to hold a {{TERM:URI}}
pointing to the photo.  You can model such an attribute after
{{EX:labeledURI}} ({{REF:RFC2079}}) or simply create a subtype,
e.g.:

>	attributetype ( 1.1.2.1.3 NAME 'x-my-PhotoURI'
>		DESC 'URI and optional label referring to a photo' 
>		SUP labeledURI )


H3: Object Class Specification

The {{objectclasses}} directive is used to define a new object
class.  The directive uses the same Object Class Description
(as defined in {{REF:RFC4512}}) used by the objectClasses
attribute found in the subschema subentry, e.g.:

E:	objectclass <{{REF:RFC4512}} Object Class Description>

where Object Class Description is defined by the following
{{TERM:ABNF}}:

>	ObjectClassDescription = "(" whsp
>		numericoid whsp      ; ObjectClass identifier
>		[ "NAME" qdescrs ]
>		[ "DESC" qdstring ]
>		[ "OBSOLETE" whsp ]
>		[ "SUP" oids ]       ; Superior ObjectClasses
>		[ ( "ABSTRACT" / "STRUCTURAL" / "AUXILIARY" ) whsp ]
>			; default structural
>		[ "MUST" oids ]      ; AttributeTypes
>		[ "MAY" oids ]       ; AttributeTypes
>		whsp ")"

where whsp is a space ('{{EX: }}'), numericoid is a globally unique
OID in dotted-decimal form (e.g. {{EX:1.1.0}}), qdescrs is one or more
names, and oids is one or more names and/or OIDs.


H4: x-my-PhotoObject

To define an {{auxiliary}} object class which allows
x-my-Photo to be added to any existing entry.

>	objectclass ( 1.1.2.2.1 NAME 'x-my-PhotoObject'
>		DESC 'mixin x-my-Photo'
>		AUXILIARY
>		MAY x-my-Photo )


H4: x-my-Person

If your organization would like have a private {{structural}}
object class to instantiate users, you can subclass one of
the existing person classes, such as {{EX:inetOrgPerson}}
({{REF:RFC2798}}), and add any additional attributes which
you desire.

>	objectclass ( 1.1.2.2.2 NAME 'x-my-Person'
>		DESC 'my person'
>		SUP inetOrgPerson
>		MUST ( x-my-UniqueName $ givenName )
>		MAY x-my-Photo )

The object class inherits the required/allowed attribute
types of {{EX:inetOrgPerson}} but requires {{EX:x-my-UniqueName}}
and {{EX:givenName}} and allows {{EX:x-my-Photo}}.

!if 0
H2: Transferring Schema

Since the {{slapd.conf}}(5) schema directives use {{REF:RFC4512}}
format values, you can extract schema elements published by any
{{TERM:LDAPv3}} server and easily construct directives for use with
{{slapd}}(8).

LDAPv3 servers publish schema elements in special {{subschema}}
entries (or subentries).  While {{slapd}}(8) publishes a single
subschema subentry normally named {{EX:cn=Subschema}}, this behavior
cannot be expected from other servers.  The subschema subentry
controlling a particular entry can be obtained by examining the
{{EX:subschemaSubentry}} attribute contained in the entry at the
root of each administrative context.  For example,

>	ldapsearch -LLL -x -b "dc=example,dc=com" -s base "(objectclass=*)" subschemaSubentry

To obtain the schema from a subschema subentry, you can use
ldapsearch(1) as follows (replace the search base as needed):

>	ldapsearch -LLL -x -b "cn=Subschema" -s base "(objectclass=subschema)" attributeTypes objectClasses

where "cn=Subschema" is the value of subschemaSubentry returned in
the prior search.

This will return {{TERM:LDIF}} output containing many type/value
pairs.  The following is an abbreviated example:

>	dn: cn=Subschema
>	objectClasses: ( 1.1.2.2.2 NAME 'x-my-Person' DESC 'my person' SUP inet
>	 OrgPerson MUST ( x-my-UniqueName $ givenName ) MAY x-my-Photo )
>	attributeTypes: ( 1.1.2.1.1 NAME 'x-my-UniqueName' DESC 'unique name wi
>	 th my organization' EQUALITY caseIgnoreMatch SUBSTR caseIgnoreSubstrin
>	 gsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 SINGLE-VALUE )
>	attributeTypes: ( 1.1.2.1.2 NAME 'x-my-Photo' DESC 'a photo (applicatio
>	 n defined format)' SYNTAX 1.3.6.1.4.1.1466.115.121.1.40

Capture the output of the search in a file and then edit the file:

+ to contain only desired type/value pairs
^ join LDIF continuation lines
^ replace attribute type with directive name
(e.g. {{EX:s/attributeTypes:/attributeType /}} and
{{EX:s/objectClasses:/objectClass /}}).
^ reorder lines so each element is defined before first use
^ continue long directives over multiple lines

For the three type/value pairs in our example, the edit should
result in a file with contains of:

>	attributetype ( 1.1.2.1.1 NAME 'x-my-UniqueName'
>		DESC 'unique name with my organization' 
>		EQUALITY caseIgnoreMatch
>		SUBSTR caseIgnoreSubstringsMatch
>		SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
>		SINGLE-VALUE )
>	attributeType ( 1.1.2.1.2 NAME 'x-my-Photo'
>		DESC 'a photo (application defined format)'
>		SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
>	objectClass ( 1.1.2.2.2 NAME 'x-my-Person'
>		DESC 'my person'
>		SUP inetOrgPerson
>		MUST ( x-my-UniqueName $ givenName )
>		MAY x-my-Photo )

Save in an appropriately named file (e.g. {{F:local.schema}}).
You may now include this file in your {{slapd.conf}}(5) file.
!endif


H3: OID Macros

To ease the management and use of OIDs, {{slapd}}(8) supports
{{Object Identifier}} macros.  The {{EX:objectIdentifier}} directive
is used to equate a macro (name) with a OID.  The OID may possibly
be derived from a previously defined OID macro.   The {{slapd.conf}}(5)
syntax is:

E:	objectIdentifier <name> { <oid> | <name>[:<suffix>] }

The following demonstrates definition of a set of OID macros
and their use in defining schema elements:

>	objectIdentifier myOID	1.1
>	objectIdentifier mySNMP	myOID:1
>	objectIdentifier myLDAP	myOID:2
>	objectIdentifier myAttributeType	myLDAP:1
>	objectIdentifier myObjectClass	myLDAP:2
>	attributetype ( myAttributeType:3 NAME 'x-my-PhotoURI'
>		DESC 'URI and optional label referring to a photo' 
>		SUP labeledURI )
>	objectclass ( myObjectClass:1 NAME 'x-my-PhotoObject'
>		DESC 'mixin x-my-Photo'
>		AUXILIARY
>		MAY x-my-Photo )