A recent trend in education and in web development is to build learning environment on top of web platforms which are carefully designed to host a plurality of software components (sometimes called widgets or plugins) which can be organized or combined (mashed-up) at user's convenience to create personalized environments. The degree of personalization can depend on the role of the users such as in traditional virtual learning environment, where the components are chosen by a teacher in the context of a course. Or, it can be more opened as in a so-called personalized learning environment (PLE), for instance as in the case of a personalized homepage hosed on a portal such as Netvibes. It now exists a wide array of available web platforms exhibiting different functionalities but all built on the same concept of aggregating components together to support different tasks and scenarios. This article shows that recent developments and standardization efforts allow to map the functionality of these platforms onto more or less independent dimensions which are becoming the building blocks for constructing a personal learning environment.