user9382: A largely abstract question (set) I've tried to answer for awhile is the nature of a TxID (32 byte hex Transaction ID hash).
First and foremost, I certainly understand the main function if this value(?) is to uniquely identify a Transaction (primarily to tracks unspent outputs, AKA UTXOs).
But let's take a random TxID, say e151de4f5a339ed545e24ecfc8f811f9143fefc10574af40721a156ff2d3a389. 

How is a TxID assigned to a Transaction?
Are 2 identical Txs that: double spend, have identical k PRNG-signed (so not a RNG!) sigs, identical inputs/outputs (a lot of assumptions here) given identical hashes?
Tangentially: are the Big/Little Endian expressions of TxIDs (by BCI and bitcoincore respectively) suggesting two different usages (ie TxIDs are values in one sense but akin to URIs in another: is this normal?)

I know the questions seem somewhat disparate but I think the best summation is what exactly are TxIDs?

user85: 
How is a TxID assigned to a Transaction?

It's a hash of key transaction information -- inputs, outputs, scripts, signatures.

Are 2 identical Txs that: double spend, have identical k PRNG-signed (so not a RNG!) sigs, identical inputs/outputs (a lot of assumptions here) given identical hashes?

This question is ill-formed. Unless there's some difference between them, they're not 2 transactions, they're one transaction. It's like talking about "two identical integers" -- that would just be one integer.

9382: <p>A largely abstract question (set) I've tried to answer for awhile is the nature of a TxID (32 byte hex Transaction ID hash).</p>

<p>First and foremost, I certainly understand the main function if this value(?) is to <em>uniquely identify a Transaction</em> (primarily to tracks unspent outputs, AKA UTXOs).</p>

<p>But let's take a random TxID, say <a href="https://blockchain.info/tx/e151de4f5a339ed545e24ecfc8f811f9143fefc10574af40721a156ff2d3a389" rel="nofollow"><em>e151de4f5a339ed545e24ecfc8f811f9143fefc10574af40721a156ff2d3a389</em></a>. </p>

<ol>
<li>How is a TxID assigned to a Transaction?</li>
<li>Are 2 identical Txs that: double spend, have identical <em>k</em> PRNG-signed (so not a RNG!) sigs, identical inputs/outputs (a lot of assumptions here) given identical hashes?</li>
<li>Tangentially: are the Big/Little Endian expressions of TxIDs (by <a href="http://blockchain.info" rel="nofollow">BCI</a> and bitcoincore respectively) suggesting two different usages (ie TxIDs are values in one sense but akin to URIs in another: is this normal?)</li>
</ol>

<p>I know the questions seem somewhat disparate but I think the best summation is <strong>what <em>exactly</em> are TxIDs?</strong></p>
 85: <blockquote>
  <p>How is a TxID assigned to a Transaction?</p>
</blockquote>

<p>It's a hash of key transaction information -- inputs, outputs, scripts, signatures.</p>

<blockquote>
  <p>Are 2 identical Txs that: double spend, have identical k PRNG-signed (so not a RNG!) sigs, identical inputs/outputs (a lot of assumptions here) given identical hashes?</p>
</blockquote>

<p>This question is ill-formed. Unless there's some difference between them, they're not 2 transactions, they're one transaction. It's like talking about "two identical integers" -- that would just be one integer.</p>
