Multiple Digital Signatures
Either a model or a file can contain multiple and unlimited signatures.
Adding a new signature does not invalidate existing signatures, although one signature can be valid while others are invalid. Support for multiple signatures means that more than one person can add his signature to a single model or file. Or that one person can sign one model in several places. Since each signature has its own verified status, you can add a new signature after a previous signature has been invalidated by a change to the model or file. This is like initiating a change. The Digital Signatures dialog is useful for detecting and locating signatures in a model or file.
Sometimes a user can sign only after others sign. When a new signature certifies both the file content and other signatures, it is sometimes called "countersigning" but in Bentley View it is referred to as a "signature hierarchy."
A hierarchy captures signing order and also records which signatures are required as prerequisites for a new signature. The new signature depends on these prerequisite signatures and is invalidated if a prerequisite signature is deleted or otherwise invalidated. When this happens, the (new) dependent signature remains invalid, even if the prerequisite signature is re-validated. This preserves signing order. Nested hierarchies can be created so that a new signature becomes dependent on a signature that already has prerequisite dependencies. There are no structural limitations to the depth of a signature hierarchy. One signature can be a prerequisite of several dependent signatures so that hierarchies overlap (defining a graph rather than a tree). The Digital Signatures dialog visually displays hierarchy relationships.
A signature hierarchy is the only true proof of signing order. Signature dates is not a reliable indicator of signing order for several reasons: