What is the difference between the Data Mapper, Table Data Gateway (Gateway), Data Access Object (DAO) and Repository patterns?

Your example terms; DataMapper, DAO, DataTableGateway and Repository, all have a similar purpose (when I use one, I expect to get back a Customer object), but different intent/meaning and resulting implementation.

A Repository "acts like a collection, except with more elaborate querying capability" [Evans, Domain Driven Design] and may be considered as an "objects in memory facade" (Repository discussion)

A DataMapper "moves data between objects and a database while keeping them independent of each other and the mapper itself" (Fowler, PoEAA, Mapper)

A TableDataGateway is "a Gateway (object that encapsulates access to an external system or resource) to a database table. One instance handles all the rows in the table" (Fowler, PoEAA, TableDataGateway)

A DAO "separates a data resource's client interface from its data access mechanisms / adapts a specific data resource's access API to a generic client interface" allowing "data access mechanisms to change independently of the code that uses the data" (Sun Blueprints)

Repository seems very generic, exposing no notion of database interaction. A DAO provides an interface enabling different underlying database implementations to be used. A TableDataGateway is specifically a thin wrapper around a single table. A DataMapper acts as an intermediary enabling the Model object to evolve independently of the database representation (over time).

There is a tendency in software design world (at least, I feel so) to invent new names for well-known old things and patterns. And when we have a new paradigm (which perhaps slightly differs from already existing things), it usually comes with a whole set of new names for each tier. So "Business Logic" becomes "Services Layer" just because we say we do SOA, and DAO becomes Repository just because we say we do DDD (and each of those isn't actually something new and unique at all, but again: new names for already known concepts gathered in the same book). So I am not saying that all these modern paradigms and acronyms mean EXACTLY the same thing, but you really shouldn't be too paranoid about it. Mostly these are the same patterns, just from different families.

Data Mapper vs Table Data Gateway To make a long story short: