# $OpenLDAP$ # Copyright 1999-2021 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 { | [:] } 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 )