A personalknowledge base is an electronic tool used to express, capture, and later retrieve the personal knowledge of an individual. It differs from a traditional database in that it contains subjective material particular to the owner, that others may not agree with nor care about. Importantly, a PKB consists primarily of knowledge, rather than information; in other words, it is not a collection of documents or other sources an individual has encountered, but rather an expression of the distilled knowledge the owner has extracted from those sources. The term personal knowledge base was mentioned as early as the 1980s, but the term came to prominence when it was described at length in publications by computer scientistStephen Davies and colleagues, who compared PKBs on a number of different dimensions, the most important of which is the data model that each PKB uses to organize knowledge. Davies and colleagues examined three aspects of the data models of PKBs:
their, which prescribes rules about how knowledge elements can be structured and interrelated ;
their, or basic building blocks of information that a user creates and works with, and the level of granularity of those knowledge elements ; and
their, which involves the level of formal semantics introduced into the data model.
Davies and colleagues also differentiated PKBs according to their architecture: file-based, database-based, or client–server systems. Non-electronic personal knowledge bases have probably existed in some form for centuries: Da Vinci's notebooks are a famous example. More commonly, files of index cards, edge-notched cards and annotatedprivate libraries, have served this function in the pre-electronic age. Undoubtedly the most famous early formulation of an electronic PKB was Vannevar Bush's description of the "memex" in 1945. In a 1962 technical report, human–computer interactionpioneerDouglas Engelbart described his use of edge-notched cards to partially model Bush's memex.
Examples
Davies and colleagues mentioned the following as examples of software applications that have been used to build PKBs: ;Open source