These techniques both place assemblages of artefacts into relative order.
Petrie used sequence dating to work back from the earliest historical phases of Egypt into pre-dynastic Neolithic times, using groups of contemporary artefacts deposited together at a single time in graves.
It must be made clear at the outset that typology is not, strictly speaking, a dating method, but a means of placing artefacts into some kind of order.
Classification divides things up for the purposes of description, whereas typology seeks to identify and analyse changes that will allow artefacts to be placed into sequences.
The first successful application was to clay fired to make pottery, but it is commonly used now for dating flint tools that have been burnt, for example by being dropped accidentally into a fire.