Legion Context Space

All Legion objects are automatically assigned a unique system-level identifying name called a Legion Object Identifier (LOID). The LOID enables Legion to find, control, and move Legion objects scattered over several different machines. But since LOIDs consist of several lines of numbers, you can map one or more simple string names--context names--to a LOID and use that name instead.

Objects contain in their state a root context (implicitly named /) that provides each object with a base for absolute path names. The root context's LOID is stored in a variable that can altered by the object at runtime. Objects also contain in their state the current context's LOID, which provides the basis for relative context paths. It is important to note that this default path service provided by the Legion library is completely replaceable. For example, if a user wished to manipulate context spaces via DOS-style "\" delimited path names, the service could easily be implemented using the primitive context manipulation routines provided by the Legion library.

About the LOID

A LOID is a variable length binary structure (typically more than 128 bytes), which contains a type field followed by several variable size fields. The first variable field indicates the Legion domain in which the LOID was created, the second is the class identifier, the third is the instance number, and the fourth is a public key. The type, domain, and class identifier fields must be present. A LOID may be appended with any number of other fields, each of whose size and meaning are dependent on the LOID type. LOIDs are represented as strings, using standard "dotted hex" notation. For example, a typical LOID would look something like this:

1.01.07.01.000001fc0d24ab3512f63533f3f96b2bba0572aed8d47efec
7c24618fca3a3d49326fa84eaa320724c10264f225c97820aced74586
194974256ee86c2ae0565d55c8e623

In this LOID, the type field, 1, indicates the LOID's type; the first variable field, 01, indicates the domain in which the object was created; the second variable field, 07, indicates the class that the object belongs to; the third variable field, 01, indicates the object's instance number; and the fourth variable field, 000001fc0d24ab..., is the object's RSA public key. This breakdown is shown here:

This notation is obviously too cumbersome for most users to manipulate as strings, so the naming service provided by context spaces allows users to deal with objects using meaningful string names chosen by the user. This separation of concerns between system-level names and user-level names allows Legion LOIDs to contain system-level information, such as an object's public key, without polluting the user-level name-space.