openldap/doc/guide/admin/schema.sdf

# $OpenLDAP$
# Copyright 1999-2000, The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.

H1: Schema Specification

This chapter describes how to extend the schema used by {{slapd}}(8).
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

H2: Distributed Schema Files

OpenLDAP 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 6.1: 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)
nadf.schema		North American Directory Forum (FYI)
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
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
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 attribute types and object classes
using the syntaxes and matching rules already supported by slapd.
slapd can also be extended to support additional syntaxes
and matching rules, but this requires some programming and hence
is not discussed here.

There are five steps to defining new schema:
^	obtain Object Identifer
+	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 6.2: 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	myAttribute
1.1.2.2		ObjectClasses
1.1.2.2.1	myObjectClass
!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 a
something more sophisticated such as the {{OpenLDAP OID Registry}}
({{URL:http://www.openldap.org/faq/index.cgi?file=197}}).

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

.{{Under no circumstances should you use a fictious OID!}} 

To obtain a fully registered OID at {{no cost}}, apply for
an OID under {{ORG[expand]IANA}} (IANA) maintained
{{Private Enterprise}} arch.  Any private enterprise (organization)
may request an OID to be assigned under this arch.  Just fill
out the {{ORG:IANA}} form at {{URL: http://www.iana.org/cgi-bin/enterprise.pl}}
and your official OID 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}} were {{EX:X}}
is an integer.

Note: Don't let the "MIB/SNMP" statement on the IANA page confuse you.
OIDs obtained using this form may be used for any purpose including
identifying LDAP schema elements.


H3: Name Prefix

In addition to assigning a unique object identifier to each schema
element, you should provide a least one textual name for each
element.  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.

To reduce (but not eliminate) the potential for name clashes,
the convention is to prefix names of non-Standard Track with
a few letters to localize the changes to your organization.
The smaller the organization, the longer your prefix should
be.

In the examples below, we have choosen a short prefix '{{EX:my}}'
(to save space).  Such a short prefix would only be suitable for
a very large, global organization.  For a small, local organization,
we recommend something like '{{EX:deFirm}}' (German company) or
'{{EX:comExample}}' (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:RFC2252}}) used by the attributeTypes
attribute found in the subschema subentry, e.g.:

E:	attributetype <{{REF:RFC2252}} Attribute Type Description>

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

>      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 ] ; see section 4.3
>          [ "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:1.2.3}}), qdescrs is one or more
names, woid is either the name or OID, and noidlen is an optional 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'
>		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' ) SUP name )

Notice that each defines the attribute's OID and descriptive
names.  Each name is an alias for the OID.  {{slapd}}(8) returns
the first listed name when returning results.

The first attribute, {{EX:name}}, has a syntax of {{EX:directoryString}}
(a UTF-8 encoded Unicode string) with a recommend maximun length.
Note that syntaxes are specified by OID.  In addition, the equality
and substring matching uses case ignore rules.  Below are tables 
listing commonly used supported syntax and matching rules.

!block table; align=Center; coltags="EX,EX,N"; \
	title="Table 6.3: Supported Syntaxes"
Name			OID				Description
binary			1.3.6.1.4.1.1466.115.121.1.5	BER/DER data
boolean			1.3.6.1.4.1.1466.115.121.1.7	boolean value
distinguishedName	1.3.6.1.4.1.1466.115.121.1.12	DN
directoryString		1.3.6.1.4.1.1466.115.121.1.15	UTF-8 string
IA5String		1.3.6.1.4.1.1466.115.121.1.26	ASCII string
Integer			1.3.6.1.4.1.1466.115.121.1.27	integer
Name and Optional UID	1.3.6.1.4.1.1466.115.121.1.34	DN plus UID
Numeric String		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
Octet String		1.3.6.1.4.1.1466.115.121.1.40	arbitary octets
Printable String	1.3.6.1.4.1.1466.115.121.1.44	printable string
!endblock

> 

!block table; align=Center; coltags="EX,N"; \
	title="Table 6.4: Supported Matching Rules"
Name				Type		Description
booleanMatch			equality	boolean
objectIdentiferMatch		equality	OID
distinguishedNameMatch		equality	DN
uniqueMemberMatch		equality	DN with optional UID
numericStringMatch		equality	numerical
numericStringOrderingMatch	ordering	numerical
numericStringSubstringsMatch	substrings	numerical
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
caseIgnoreIA5Match		equality	case insensitive, space insensitive
caseIgnoreIA5OrderingMatch	ordering	case insensitive, space insensitive
caseIgnoreIA5SubstringsMatch	substrings	case insensitive, space insensitive
caseExactIA5Match		equality	case sensitive, space insensitive
caseExactIA5OrderingMatch	ordering	case sensitive, space insensitive
caseExactIA5SubstringsMatch	substrings	case sensitive, space insensitive
!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 and both are
meant for usage by user applications.  You likely won't need to
specify other parameters such as {{EX:OBSOLETE}}.

The following subsections provide a couple of examples.


H4: myUniqueName

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 'myUniqueName'
>		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 included 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 'myUniqueName'
>		DESC 'unique name with my organization' 
>		SUP name )


H4: myPhoto

Many organizations maintain a photo of each each user.  A
{{EX:myPhoto}} 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 'myPhoto'
>		DESC 'a photo (application defined format)' 
>		SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
>		SINGLE-VALUE )

As noted in the description, LDAP has no knowledge of the
format of the photo.  It's assumed 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}}).


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:RFC2252}}) used by the objectClasses
attribute found in the subschema subentry, e.g.:

E:	objectclass <{{REF:RFC2252}} Object Class Description>

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

>	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 numeric form (e.g. {{EX:1.2.3}}), qdescrs is one or more
names, and oids is one or more names and/or OIDs.


H4: myPhotoObject

To define an {{auxiliary}} object class which allows
myPhoto to be added to any existing entry.

>	objectclass ( 1.1.2.2.1 NAME 'myPhotoObject'
>		DESC 'mixin myPhoto'
>		AUXILIARY
>		MAY myPhoto )


H4: myPerson

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 'myPerson'
>		DESC 'my person'
>		SUP inetOrgPerson
>		MUST ( 'myUniqueName' $ 'givenName' )
>		MAY 'myPhoto' )

The object class inherits the required/allowed attribute
types of {{EX:inetOrgPerson}} but requires {{EX:myUniqueName}}
and {{EX:givenName}} and allows {{EX:myPhoto}}.

!if 0
H2: Transferring Schema

Since the {{slapd.conf}}(5) schema directives use {{REF:RFC2252}}
format values, you can extract schema elements published by
any LDAPv3 server and easily construct directives for use with
{{slapd}}(8).

LDAPv3 servers publish schema elements in special {{subschema}}
entries (or subentries).  {{slapd}}(8) publishes a single subschema
entry normally named {{EX:cn=Subschema}}.  In a server which
supports a single subschema subentry, the DN of the subschema
subenty can usually be found by examining the value of the
{{EX:subschemaSubentry}} attribute type in the {{root DSE}}.
Other servers may publish multiple subschema entries.  These
can be located by examining the {{EX:subschemaSubentry}} attribute
contained in the entry at the root of each administrative context.

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

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

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

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/}}).
^ 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 'myUniqueName'
>		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 'myPhoto'
>		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 'myPerson'
>		DESC 'my person'
>		SUP inetOrgPerson
>		MUST ( 'myUniqueName' $ 'givenName' )
>		MAY 'myPhoto' )

Save in an appropriately named file (e.g. {{F:my.schema}}).
You may now include this file in your {{slapd.conf}}(8) file.
!endif