JEAN is a system for organising and making the most efficient use of the data and tools that you have on your computer. When you have a collection of items on your computer, for example music, images or documents, then you need to: classify each item into one or more categories; group items together, either because they belong naturally together as a group or as a temporary expedient; define certain properties or attributes of each item; find items quickly and easily by looking in categories and/or inspecting attributes and perform an appropriate action on one or a group of items.
For example, if you are maintaining a collection of music, each track will exist as a separate file on your computer's disk. Each piece of music can be classified by its genre, e.g. rock, folk, classical. Many pieces can be placed into more than one genre, for example folk and rock. Many genres are subcategories of others, so that folk-rock could be a subcategory of rock and also of folk.
Pieces of music are naturally grouped by the album on which they were released, they may also be grouped temporarily into a playlist or more permanently into a compilation.
Each piece of music has a number of attributes: its title, composer or writer, performer (either an individual, a band, or an orchestra with conductor and soloist), etc.. Some of these same attributes can also be applied to albums.
We can look for music in a number of ways, by the title of a track or album, the performer or just by genre. We need to be able to expand categories into subcategories and descend through albums to the tracks we want. We may just remember some detail so that we can search for all items which have that particular value or values in one of their attributes and then be presented with a manageable list from which to select.
Finally of course, having selected one or more pieces of music we want to be able to play them, possibly in a particular order.