This is a practical consequence of the first and second characteristics. This is important, as a relational database is a general purpose tool, which can be used to deal with a very wide range of problems. Generally, multiple databases do not share common schema. It is the first characteristic, which is the key benefit of a relational system, which cannot be provided by a directory. For example if there is a corporate database which holds people information, and each entry holds both manager and location, it would be natural and efficient in a relational database to find 'all of the people whose managers are located in New York'.
Objects are essentially independent in the directory, and linked into a hierarchy.
It is this independence which enables straightforward distributed provision. There is a fixed core schema for naming basic types of objects and managing them in a hierarchy. This common core is key to making a directory 'hang together'. The schema for separate objects in the directory is highly flexible and extensible. It is the first characteristic that is the key benefit of a directory, which cannot be provided by a relational database.