Pre-digital era

• notebooks,
• library classification;

PC era

• digital documents,
• "file" system;

Web era

• webpage,
• "personal wiki"
  • gollum,
  • DokuWiki,
  • wikidPad

AI era

• search bar,
• NLP stacks (Solr)
  • search engine,
  • clustering.

Functionality Need

• powerful search engine (Lucene)
  • rich document indexing (Tika)
  • auto-completion, spell check
  • entry suggestion
• dynamic clustering and labeling by document topics
  • integrating note snippets into specific "views", which facilitates long-form writing.
  • visualization: treemap (FoamTree), network
• navigation: facets, breadcrumbs
• cross-referencing / hyperlinking

Tailoring for personal knowledge pool

• Data models (mostly schema-less natural language): .txt, .md, .docx, .pptx, .xlsx, .pdf, .html
  • minimal tailoring of legacy document markups and schemas.
  • users should be editing note contents, not HTML files.

Tailoring for personal knowledge pool

• PKM use cases (against the global knowledge space)
  • logs: Snippets of notes "in sack" for in-depth documenting.
  • notes: Personally organized notes, beyond one-step reach of Google search.
  • literature: References for attribution. [Significant for critical writing.]

Indexing

• Indexing rich documents with Apache Tika.
• Apache Tika has a wide spectrum of supported formats.

Clustering

• Carrot² is a document thematic clustering engine, written in Java and distributed under the BSD license.
  • Clustering algorithms: Lingo, STC, Lingo3G™. 
  • Visualization: FoamTree, Circles
  • Search feeds: Lucene, Solr, other search APIs.
• Front-ends
  • Carrot² Web Application
  • Carrot² Document Clustering Workbench

Web UI

• Velocity Search UI [built-in]
• Project Blacklight, a Ruby on Rails Engine plugin.
• Lucidworks Fusion, a platform for building enterprise search applications.