How does this たる function in this JLPT sentence?


Please bear with me as I reveal my tenuous grasp on advanced grammar...

While studying for the Grammar section of the JLPT (N1) I came across this
grammar point to study: `たる`

I came across a lot of confusion trying to sort out exactly what it means.
Dispite the lack of solid explanations at my favorite haunts, I found out that
for all intents and purposes there are two kinds of `たる`, one that is related
to adjectives like what is discussed in this [JLU
question](https://japanese.stackexchange.com/questions/1013/what-exactly-is-a-
taru-adjective), and another that is appended to "a regular noun and modifying
another noun", like how Akibare describes in [this
thread](http://linguaphiles.livejournal.com/2144558.html?thread=40448558).

It's the latter that will be tested on the JLPT.

From [tanos.co.uk](http://www.tanos.co.uk/jlpt/jlpt1/grammar/usage/):

> ~たる
>
> 意味： Be~ ; As a~ ; is~
>
> 接続： [名]＋たる＋[名]
>
> 例文： 教師たる者、学生に対して常に公平であるべきだ。

My grammar study books says that it is used with `身分や職業を表す｢名詞｣`.

* * *

I thought I had it figured out, then I came across this sentence from a past
test (1998):

> 相手を十分納得させるに **たる** データを示す必要がある。

I believe it means "It is necessary that we have data that will sufficiently
convince the other party." What I can't understand is how `たる` fits into it.

Does `...納得させるに` function as a noun? If so, it doesn't seem to be referring to
a noun that shows social position or occupation.

Is this an example of the first usage of `たる` (which to be honest I don't
really understand)?




> 「相手を十分納得させるに **たる** データを示す必要がある。」

This たる is "足る", "足りる" = to be enough/sufficient

「させるに」is not a noun. I think it's a shortened form of 「させるのに」or 「させるために」. So
the sentence could be rephrased as:

「相手を十分納得させるのに足りるだけの量のデータを示す必要がある。」  
「相手を十分納得させるのに足りるだけのデータを示す必要がある。」  
「相手を十分納得させるのに足りる量のデータを示す必要がある。」  
「相手を十分納得させるのに十分な(量の)データを示す必要がある。」




> 「相手を十分納得させるに **たる** データを示す必要がある。」

This たる is "足る", "足りる" = to be enough/sufficient

「させるに」is not a noun. I think it's a shortened form of 「させるのに」or 「させるために」. So
the sentence could be rephrased as:

「相手を十分納得させるのに足りるだけの量のデータを示す必要がある。」  
「相手を十分納得させるのに足りるだけのデータを示す必要がある。」  
「相手を十分納得させるのに足りる量のデータを示す必要がある。」  
「相手を十分納得させるのに十分な(量の)データを示す必要がある。」

