An archaeological relationship is the position in space and by implication, in time, of an object or context with respect to another. This is determined, not by linear measurement but by determining the sequence of their deposition – which arrived before the other. The key to this is stratigraphy.
Archaeological material would, to a very large extent, have been called rubbish when it was left on the site. It tends to accumulate in events. A gardener swept a pile of soil into a corner, laid a gravel path or planted a bush in a hole. A builder built a wall and back-filled the trench. Years later, someone built a pig sty onto it and drained the pig sty into the nettle patch. Later still, the original wall blew over and so on. Each event, which may have taken a short or long time to accomplish, leaves a context, a deposit of material, on the site. This deposit and its relationship to earlier contexts may show up in section or in plan when viewed from above.
When there are hundreds of these relationships, a formal method of keeping track of them is required. An effective method is to prepare a Harris matrix. Their position in the matrix places the contexts in their sequence in time. Provided the archaeologist has maintained a record of the context in which each artefact was found, the tracing of the contexts by the matrix does equally well for the artefacts (objects).
Terminology in archaeology is not definitive but the following are typical uses of terms:
A relationship that is later in the sequence is sometimes referred to as "higher" in the sequence and a relationship that is earlier "lower" though the term higher or lower does not itself imply a context needs to be physically higher or lower. It is more useful to think of this higher or lower term as it relates to the contexts position in a Harris matrix which is a two dimensional representation of a sites formation in space and time.