一方作为合同的“见证人”是什么意思，其含义是什么？

Question

我正在做一些练习来了解 Daml，其中一个练习涉及将资产从一方转移到另一方。一切正常，但我注意到之前资产合约的所有者被标记为新资产合约的“见证人”（在 Assets.Asset:Asset，ID 为 #8:2 的合约有 Alice 标有 W、Witness).

我对此很感兴趣。一方作为合同的“见证人”是什么意思，它的含义是什么？我没有在文档中找到答案…

这是我使用过的一些代码。我已经应用了提议-接受模式。

template HolderRole
  with
    operator : Party
    holder : Party
  where
    signatory operator, holder
    key (operator, holder) : (Party, Party)
    maintainer key._1

    controller holder can
      nonconsuming ProposeAssetTransfer : ContractId AssetTransferProposal
        with
          receiver : Party
          assetCid : ContractId Asset
        do
          exercise assetCid ProposeTransfer with receiver
      
      nonconsuming AcceptAssetTransfer : ContractId Asset
        with
          assetTransferProposalCid : ContractId AssetTransferProposal
        do
          exercise assetTransferProposalCid AssetTransferProposal_Accept

template Asset
  with
    issuer : Party
    owner : Party
    symbol : Text
    quantity : Decimal
  where
    signatory issuer, owner

    controller owner can
        ProposeTransfer : ContractId AssetTransferProposal
      with
        receiver : Party
      do
        create AssetTransferProposal with receiver, asset = this, assetCid = self

template AssetTransferProposal
  with
    receiver : Party
    asset : Asset
    assetCid : ContractId Asset
  where
    signatory asset.owner, asset.issuer

    controller receiver can
      AssetTransferProposal_Accept : ContractId Asset
        do
          create asset with owner = receiver

assetTransferTest = script do
  ...

  -- Transfer an Asset to another Party
  assetTransferProposalCid <- submit alice do
    exerciseByKeyCmd @HolderRole (operator, alice) ProposeAssetTransfer
      with receiver = bob, assetCid = assetCid

  -- Accept a transfer
  submit bob do
    exerciseByKeyCmd @HolderRole (operator, bob) AcceptAssetTransfer
      with assetTransferProposalCid = assetTransferProposalCid

Answer 1

这意味着 Alice 看到了新合约 (#8:2) 的创建，因为她是旧合约 (#6:2) 在被消费时的一方Bob 在 HolderRole 上锻炼 AcceptAssetTransfer。其含义是 Alice 可以看到 Bob 成为 Asset 的新所有者，但不会看到涉及 Asset 的任何未来事件，例如由于将资产发送给另一方。

此外，即使 Alice saw/witnessed 新合同的创建，她也无法在她目睹的一次性事件后查询它。

有时文档有点难以搜索，所以这里有一些相关链接：

因为在我们的论坛上也有人同时问了这个问题further discussion may be located here。

一方作为合同的“见证人”是什么意思，其含义是什么？

What means a Party being a ‘Witness’ of a contract and what are its implications?

daml