Hypermapped Virtual World Query

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To extract 3 time slices from a hypermapped virtual world R the query in mathematical notation is: St (t1, t2, t3) R

In SQL-like language the query can be expressed as:

SELECT     t
CLUSTER    t1, t2, t3
FROM       R

Each cluster can be "open" (objects inside visible) or "closed" (objects inside not visible). The notation is t2o for an open cluster and t2c or simply no superscript for a closed cluster. In the SQL-like language the keyword "OPEN" is used:

SELECT     t
CLUSTER    t1,  OPEN t2, t3
FROM       R