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Executive Summary

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(This is the page you show to your management to get the on board with using an X.500 directory. It intentionally abstains from the more technical details of X.500 directories.) For an overview for a more general audience, see the Intro.

The X.500 directory is a technology for producing a global, distributed database (although it can be used exclusively privately as well). It is "distributed" in the sense that the data can be split across a nearly infinite number of independent servers.

The way that data is represented in an X.500 directory lends itself to great flexibility. An X.500 directory has features that make it like a time-series database, a graph database, a document-oriented database, and a relational database, all in one. It is designed primarily to store information about people and organizations, but it can store any kind of data.

The Problem It Solves​

Databases already exist, and they already have access controls, sharding, authentication, integrity at rest, and so on. However, many organizations still feel the need to put a REST API between end users and the database, which demonstrates some fundamental shortcoming of existing solutions. Existing solutions fall short in these respects, in which X.500 directories excel:

  1. Standardized implementations with expectations of interoperability. X.500 is a series of standards. Implementations of X.500 directories are generally interoperable, if well-constructed. There is no "MySQL standard" or "Postgres standard" where you could implement your own alternative and expect future compatibility with all other implementations. Abundance of implementations means more options, better security, and a better ecosystem.
  2. Advanced access controls. In many databases, access controls can constrain who has access to particular collections, documents, columns, tables, and so on, but X.500 directories can regulate specific values, use groups as layer of indirection, and regulate complex selections of the data.
  3. Designed to be split across domains of trust. Unlike database sharding, X.500 directories are designed to confederate data across the organizational boundary. Organizations can share their data, and even let others modify it, but control who, how, when, and so on.
  4. Directly usable by end users. Traditional databases often store or present data in a format that is not directly usable by end users. For this reason, custom REST APIs and web apps are created to convert a mess of relational tables into composed, meaningful "objects" representing real world things. In X.500 directories, the data is already stored in this manner: X.500 directories model data as real world things, and they are browseable by human-friendly names like CN=Jonathan M. Wilbur rather than UUIDs or serial numbers. You do not need to re-invent the wheel when you already have a Porsche waiting for you.
  5. Standardized schema. How one organization represents a "person" in a database may differ from how another organization would, but X.500 schema uses an inheritance model, whereby data can adhere to certain standardized characteristics while still being extensible and widely recognizable. If two companies that wish to merge use X.500 directories, and they have customized the schema for representing a "person," their directory implementations and directory-enabled applications can still seemlessly utilize the commonalities that are standardized for a "person entry" across substituent organizations for instance.

There are a few other benefits that are simply too technical for an executive summary, but the above should be sufficient.

The Future​

The X.500 specifications were conceived in the late 1980s by the International Telecommunications Union with the intent of creating a sort of "distributed, global phonebook," and, admittedly, they had much more traction back then. However, if you research why the enthusiasm waned, you'll find that much of it is for reasons that are no longer applicable. X.500 directories are thought of as "legacy" mistakenly: I believe they are the future. There are technologies that died off because they are objectively inferior, such as floppy disks, and there are those that were dormant for a long time simply because they were invented before their time.

Other Executive Summaries​

In addition to the above summary, other executive summaries of X.500 directory services can be found in: