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Parent Relationships

parentHashes lists the blockHash of each direct parent Block. ALX normalizes the list before computing blockHash, making the declared parent set part of deterministic Block identity. Connected Blocks form a directed derivation Graph.

Parent Normalization​

ALX normalizes parentHashes in this order:

  1. Trims surrounding whitespace and converts each hash to lowercase.
  2. Validates each hash against ^0x[a-f0-9]{64}$.
  3. Removes duplicate hashes.
  4. Sorts the remaining hashes lexicographically.
  5. Rejects more than 256 distinct hashes.

One invalid entry rejects the complete operation. Normalization never drops an entry or returns a partial parent set. createBlock() and hash derivation normalize the supplied list. validateBlock() does not normalize: a recorded Block whose parentHashes is not already normalized fails validation.

The following input and its normalized output produce the same blockHash for the same content:

{
  "input": [
    "  0x84EE19CABB89367925F79A27E0B7D43D075CB8842CE056A468DB6B7355663F5A ",
    "0x2ea8df928f1a68f3fbbbbb2ae5938e817e1633a4066590cd2b22f6fa526aa8aa",
    "0x84ee19cabb89367925f79a27e0b7d43d075cb8842ce056a468db6b7355663f5a"
  ],
  "normalized": [
    "0x2ea8df928f1a68f3fbbbbb2ae5938e817e1633a4066590cd2b22f6fa526aa8aa",
    "0x84ee19cabb89367925f79a27e0b7d43d075cb8842ce056a468db6b7355663f5a"
  ]
}

Parent Normalization Constraints​

InputResult
Omitted parentHashes argumentTreated as an empty array
Supplied value that is not an array, including nullRejected with ALX_INVALID_HASH
Entry that is not a stringRejected with ALX_INVALID_HASH
Entry that does not match ^0x[a-f0-9]{64}$ after trimming and lowercasingRejected with ALX_INVALID_HASH
More than 256 distinct parent hashes after deduplicationRejected with ALX_TOO_MANY_PARENTS

Parent Selection​

Applications declare direct parent Blocks through parentHashes.

  • Root Blocks: Use an empty parent set ([]).
  • Derived Blocks: List every direct upstream Block the new Block depends on.

Declare direct parents only. Earlier ancestors remain reachable through the derivation Graph when the required Blocks are available. See Block Identity for hash derivation.