it's just a proposal as far as I can tell. It is not detailing how Bitcoin currently works.
-As the presentation of the paper says, this is like a problem definition of the state co before they or even Utreexo proposed their model. Yes there r many many research projects but these r variations of the tree since 2010
https://bitcointalksearch.org/topic/storing-utxos-in-a-balanced-merkle-tree-zero-trust-nodes-with-o1-storage-101734Related Work
ByteCoin first proposed including the hash of the current "balance sheet" in each block (i.e., the set of available unspent tx outputs), making it possible to validate transactions without needing to store the entire blockchain. Greg Maxwell later suggested using a Merkle tree in order to query such this set more efficiently. DiThi later made an equivalent proposal. Most recently, etotheipi suggested using a self-balancing Merkle tree so that incremental modification to the structure would be more efficient. I scoured the academic literature, finding a Usenix paper from 1996 by Moni Naor and Kobbi Nissim, suggesting that a RedBlack tree could be augmented with hashes instead of pointers. I wrote a reference implementation of such an "Authenticated Data Structure". To my knowledge, it is the only available (open-source) implementation of a self-balancing hash tree.
Hash trees (of the non-balancing variety) are widely used, for example in Git and in Tahoe-LAFS.
...
From ur Bitcoin core
"height": 1,
"version": 536870912,
"merkleroot": "37c2334d0314e11d396b5465e9bc5ec7cf0155c13a47f1af2731174331b3b78d",
"tx": [
"37c2334d0314e11d396b5465e9bc5ec7cf0155c13a47f1af2731174331b3b78d"
],
In the above example, we can see the utxo represented by its txid
yes the val of the UTXO is stored in the database, but it's the UTXO that's get stored in the Merkle Tree as stated, only in this example they represented it with it's creating TX id, what if more than 1 UTXO resulted from the same TX?
However, it is their fault they should have clarified that in their example since most TXs (more than 50% I think) have more than one ouput
.
I think this part from the Utreexo paper may also clarify any mis understanding for both of us (as I'm not that familiar with SPV)
Every node in the network verifies and stores the entire state of the system. Each user of the system has a wallet, which tracks at least one UTXO, but generally several. As the number of users of the system increases, the
UTXO set grows, and the resource cost of running a node increases. This
has led to a progressively smaller proportion of users running their own
node as more users rely on light clients or on 3rd party nodes to inform
them of the state of the network. Light clients, nodes that do not store
the system state and do not validate transactions, can still obtain some assurance about transactions through Simplified Payment Verification (SPV),
which leverages Bitcoin’s Proof-of-Work and block commitment scheme to
give compact proofs of transaction inclusion into a (not necessarily valid)
blockchain.
SPV, while reducing the resource costs of operating a network node,
comes with a number of security and privacy weaknesses not present in full
nodes. SPV nodes rely on fully validating nodes to enforce the rules of the
system as they cannot do so themselves. An adversary with sufficient hashing
power can present transactions which SPV nodes will accept as confirmed,
but which will be rejected by fully validating nodes. While improving the
security and privacy of SPV is a promising area of research, this work focuses
only on fully validating nodes, and on reducing the resource requirements
to run one.
