Lexicon

A lexicon is a type of artifact once used as a portable repository for storing computerized information. They often come in the form of small, compact chips, yet despite their size, they are capable of storing an astounding amount of data. It is possible for them to carry anything from technical schematics to the captured "life essence" of any living organism.

Typically, shortly before a Prothean's death, they could choose to have their own life essence extracted and stored in such devices. In the hands of a loved one, meaningful memories salvaged from the mind of a deceased loved one may have been of particular sentimental value. In the hands of Prothean scientists, the life essence stored in a lexicon would have been enough for them to "reconstruct" the mind of the deceased for use in an artificial intelligence construct.

History
In, the last known living Prothean, , was uncovered in his pod and released by Commander Shepard and , who were investigating activity on. Amongst other ancient artifacts, Javik carried a lexicon with him. His lexicon contained his own memories of sorrow and guilt, which he kept on him so that he would be able to remember when he woke up. At first, Javik was reluctant to use the device, and Commander Shepard did not push him to do so. Because of this, Javik's mental scarring from the events of the previous Reaper invasion eventually passed, allowing him to develop a more positive outlook on life. Later on in life, he even published a series of books on Prothean society, culture, and their extinction at the hands of the Reapers. Years later, when Javik finally decided to review the contents of the lexicon, he was far more emotionally prepared and handled the return of these harsh memories much better than he would have otherwise.