database - Is this table 4NF? -

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i'm trying design database. have table follows:

tag     post     file                1                2                3        b         4 b                1 b        b         1 b        c         1 b        d         1

each post may have more 1 tag , each file may have more 1 tag. aside tags posts , files unrelated. looking @ table there going redundancy issues example post-tag pair a-a repeated 3 times unnecessarily, same post-file pair b-1. i've looked @ definitions 1nf 4nf , seems in of them.

what did miss?

i thought if table had redundancies it's not normalized. seem normalized 4nf. must have gone wrong somewhere.

based on description should break down table 2 tables model one-to-many relationship between "post , tag", , "file , tag"

post   tag       b       a       b b       b c       b d       b   file   tag 1       2       3       4       b 1       b 1       c 1       d

take @ first example here:

http://en.wikipedia.org/wiki/fourth_normal_form

it typically same case describing in question.

here's useful question too:

database normalization


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