Naming and Directory Services

Naming and Directory Services
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Naming Services

Identfier Services:
- Map human-friendly names to the identifiers of entities used by a computing system
Entity Services:
- Map human-friendly names to entities (e.g., objects) used by a computing system

Familiar Examples of Naming Services

Identifier Services:
- The Domain Name System maps machine names to IP addresses
Entity Services:
- File systems map file names to file handles/references

Toward a Formal Definition of Naming Services

Naming Convention:
- The syntax that names must follow
Binding:
- The association of a name with an entity, name of an entity, or reference to an entity
Context:
- A set of bindings

Toward a Formal Definition of Naming Services (cont.)

Naming System:
- A set of contexts (that have the same naming convention) along with a common set of operations
Naming Service:
- The functionality provided by a naming system
Namespace:
- The set of all possible names in a naming system

Directory Systems

Relationship to Naming Systems:
- A directory system is an extension of a naming system
Additional Capabilities:
- In addition to associating names with entities, they associate entities with attributes that describe the entity

Directory Systems (cont.)

An Example:
- A service that maps a human-readable name to a printer and that contains attributes of the printer (like its speed, resolution, and number of colors)
Representing Attributes:
- Attributes normally consist of an identifier and one or more values

Toward a Formal Definition of Directory Services

Directory:
- A connected set of directory objects
Directory Service:
- Provides operations for creating, adding, modifying, and removing objects (and their attributes) in a directory

Directory/Naming Services and Databases

Attributes of the Database:
- Can be flat, relational or hierarchical
- Can be distributed
- Usually performs more reads than writes
Not Required of the Database:
- Transaction rollback
- Normalization

Domains

Defined:
- A group of systems and resources that are organized by a directory/naming service (and share a common security model)
Conceptualized:
- The basic unit in a directory/naming service
Common Structures:
- Hierarchical
- Multi-master

Metadata

Defined:
- Data about data
Uses in Directory/Naming Services:
- Determine how the data are organized
- Determine what the data mean (i.e., semantics)

An Example: X.500

Participants:
- Directory System Agent - the database
- Directory User Agent (DUA) - (like WHOIS and FINGER)
Protocols:
- Directory Access Protocol (DAP) - Add, Bind, Compare, Delete, List, Modify, ModifyRDN, Read, Search
- Directory Information Shadowing Protocol (DISP) - used to exchange updates (for replication)
- Directory Operational Bindings Management Protocol (DOP) - used to establish replication agreements
- Directory System Protocol (DSP) - allows system agents to communicate with user agents

An Example: Lightweight Directory Access Protocol (LDAP)

Defined:
- DAP for TCP/IP
Lightweight?
- No, just narrower than DAP
Implementations:
- ApacheDS
- Apple Open Directory
- Fedora DIrectory Server
- IBM Tivoli Directory Server
- Microsoft Active Directory
- OpenDS

LDAP Data Interchange Format (LDIF)

Purpose:
- Describe directory information and modifications to directory information (RFC 2849)

An Example with Two Entries:


                           version: 1
dn: cn=Barbara Jensen, ou=Product Development, dc=airius, dc=com
objectclass: top
objectclass: person
objectclass: organizationalPerson
cn: Barbara Jensen
cn: Barbara J Jensen
cn: Babs Jensen
sn: Jensen
uid: bjensen
telephonenumber: +1 408 555 1212
description: A big sailing fan.

dn: cn=Bjorn Jensen, ou=Accounting, dc=airius, dc=com
objectclass: top
objectclass: person
objectclass: organizationalPerson
cn: Bjorn Jensen
sn: Jensen
telephonenumber: +1 408 555 1212

LDIF (cont.)

Important Elements:
- DN - distinguished name
- CN - canonical name
- OU - organization unit
- DC - domain component
- changetype - indicates a change record

Example of Change Records:


                           version: 1
# Add a new entry
dn: cn=Fiona Jensen, ou=Marketing, dc=airius, dc=com
changetype: add
objectclass: top
objectclass: person
objectclass: organizationalPerson
cn: Fiona Jensen
sn: Jensen
uid: fiona
telephonenumber: +1 408 555 1212

# Delete an existing entry
dn: cn=Robert Jensen, ou=Marketing, dc=airius, dc=com
changetype: delete

# Modify an entry's relative distinguished name
dn: cn=Paul Jensen, ou=Product Development, dc=airius, dc=com
changetype: modrdn
newrdn: cn=Paula Jensen
deleteoldrdn: 1

# Rename an entry and move all of its children to a new location in
# the directory tree (only implemented by LDAPv3 servers).
dn: ou=PD Accountants, ou=Product Development, dc=airius, dc=com
changetype: modrdn
newrdn: ou=Product Development Accountants
deleteoldrdn: 0
newsuperior: ou=Accounting, dc=airius, dc=com

There's Always More to Learn