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Tag-Cloud Drawing: Algorithm for Cloud Visualization

Tag-Cloud Drawing: Algorithm for Cloud Visualization. Owen Kaser, Daniel Lemire Speaker: Yi-Ching Huang 2007/07/17. Introduction. Tag cloud can represent the frequencies of a hundred items Tag cloud can be generated using images

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Tag-Cloud Drawing: Algorithm for Cloud Visualization

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  1. Tag-Cloud Drawing: Algorithm for Cloud Visualization Owen Kaser, Daniel Lemire Speaker: Yi-Ching Huang 2007/07/17

  2. Introduction • Tag cloud can represent the frequencies of a hundred items • Tag cloud can be generated using • images • browser-specific technologies (ex: ActiveX) • plugins (ex: Flash) • complex HTML (using absolute positioning) • simple HTML with inline text or tables

  3. Problem Definitions • Problems • Wasted space • Large clumps of white space • Solutions • Floorplanning / placement problem (EDA) • Hybrid of text justification (Knuth-Pass algo) and book-placement (Skiena)

  4. Cloud Layout with Inline Text • 1st algo: take an ordered list of tags and choose where to break line • Step 1: Greedy algorithm ,O(n) • Tags are added to the current line one by one, inserting a white space between them, until the line is full • Step 2: Dynamic programming ,O(n^2) • Knuth-Plass algorithm • Except that 2 things • The last line is not an exception • If a tag exceeds the maximal width, then it will be given a line of its own

  5. Cloud Layout with Inline Text • 2nd algo: reorder tags, attempting to decrease the badness • Finding an optimal ordering is NP-hard: when the required horizontal white space between tags is zero, we have the NP-hard Strip Packing Problem (SPP) • Dynamic programming to place the tags optimally and keep only the best solution • Next Fit Decreasing Height, Weight heuristic (NFDHW)

  6. Strip Packing Problem First Fit Decreasing Height (FFDH) Next Fit Decreasing Height (NFDH)

  7. Cloud Layout with Arbitrary Placement • Min-cut placement • Placement approaches in EDA • Recursively decomposes a collection of tags by bipartitioning: splitting the tags into a “left” group and a “right” group

  8. Slicing Floorplans & Slicing Tree • Slicing floorplans • Slicing tree

  9. Nested Tables for Slicing Floorplans • Trick: each internal node in the slicing tree corresponds to a 2-element table in HTML

  10. Tag Cloud with CSS

  11. Result: Tag Cloud with Inline Text

  12. Result: Tag Cloud with Arbitrary Placement

  13. Conclusion • Use simple HTML with CSS to layout tags • Two approaches for displaying tag cloud • inline text • arbitrary placement

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