Understanding and Deploying LDAP Directory Services > 7. Schema Design > Schema Maintenance and Evolution |
Schema Maintenance and EvolutionYour schema needs will change over time as you bring up new applications and find new and interesting ways to use your directory service. So far in this chapter we have generally assumed that one person or a small group of people will look after the schema for the directory service as a whole. This is a good model to follow initially, but when your directory service becomes popular and new applications are rapidly being proposed, it may be difficult to keep up with the demand for new schemas. A more decentralized approach to schema design would then be needed. After you gain some deployment experience, you may also find yourself wishing you could change some of the schema rules that you defined when you initially deployed your directory service. This is tricky, but it is possible in certain situations described later in this section. There are also some schema- related issues to be aware of when upgrading directory service software, which we discuss as well. Establishing a Schema Review BoardOne option is to allow people to define and submit a new schema to a centralized review committee to approve it before it is installed in the directory service. The main job of the review board (which can be just one or two people) is to check for inconsistencies in the schema, ensure that redundancy is not being introduced, and make sure the schema is well-defined and well-documented. This same group can also perform clerical tasks such as assigning OIDs, and it can serve as a central point for schema advice and consent . Granting Permission to Change the Schema ConfigurationIf your directory server software supports it, you may want to allow people installing new applications to perform online schema updates over LDAP. Be careful to limit the number of people who have the access rights necessary to do this; you do not want frivolous, inappropriate, or inconsistent schemas to be installed. Check with your directory server software vendor to see if online schema updates are allowed and how to control access. Changing Existing SchemasAs with all aspects of design, it is difficult to produce a perfect, complete schema design the first time. Because the use of your directory service will change over time, so will your schema needs. It may be tempting to change your defined schemas to accommodate your changing service, but proceed with caution. It is probably okay to add optional attribute types to an object class you previously defined, but it is risky to try to remove any attribute types or add required attribute types. In practice, there is usually no reason to remove attributes or add mandatory ones. If you defined an attribute type that has the wrong syntax or name , you need to define a new type but keep the old one around and transition away from it. The most important consideration when contemplating changes to an existing schema is to make sure you have thought carefully about how it affects users, directory-enabled applications, and the directory itself. Upgrading Directory Service SoftwareWhen the time comes to upgrade your directory service software, you should make sure all your schema additions are preserved during the upgrade process. Well-designed software takes care of this for you, but otherwise you need to reconfigure the new version of the software to make it aware of your schema rules. Also, the potential trouble with software upgrades is the most compelling reason not to remove any of the schemas that come preconfigured with your directory service software.
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Index terms contained in this sectiondirectoriesschemas maintaining 2nd 3rd 4th 5th 6th existing schemas changing 2nd maintaining schemas changing existing 2nd review boards updates upgrading directory service software maintenance schemas changing existing 2nd review boards updates upgrading directory service software review boards maintaining schemas schemas maintaining changing existing 2nd review boards updates upgrading directory service software software directory service upgrading updates maintaining schemas |
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