# Entities

The Züs blockchain is structured around key entities that ensure the secure and efficient execution of transactions, state updates, and consensus. 

These entities form the foundation of the decentralized storage network, enabling users to interact with the blockchain through transactions while ensuring data integrity, security, and verifiability.

This section provides an overview of the essential blockchain entities, including:

* **Block Entity:** Represents a summary of a finalized block, including its hash, miner information, round details, and cryptographic proofs.
* **Transaction Entity:** Defines how clients interact with smart contracts and other network participants, encapsulating key details such as sender, recipient, transaction type, and cryptographic signatures.
* **Transaction Confirmation:** Validates transaction finality by linking transactions to blocks and providing proof of execution.
* **Magic Block:** Governs network-wide changes by defining the active set of miners and sharders, ensuring continuity and security across view changes.

### The Block Entity

Block entity represents the summary of a block from the blockchain.

```go
type BlockSummary struct {
	Version 	      string `json:"version" msgpack:"_v"`
	CreationDate 	      common.Timestamp `json:"creation_date"`
	Hash                  string        `json:"hash"`
	MinerID               datastore.Key `json:"miner_id"`
	Round                 int64         `json:"round"`
	RoundRandomSeed       int64         `json:"round_random_seed"`
	StateChangesCount     int           `json:"state_changes_count"`
	MerkleTreeRoot        string        `json:"merkle_tree_root"`
	ClientStateHash       util.Key      `json:"state_hash"`
	ReceiptMerkleTreeRoot string        `json:"receipt_merkle_tree_root"`
	NumTxns               int           `json:"num_txns"`
	*MagicBlock           `json:"maigc_block,omitempty" msgpack:"mb,omitempty"`
}
```

<table><thead><tr><th width="242">Field</th><th>Description</th></tr></thead><tbody><tr><td>version</td><td>Version of the block. Latest is "1.0".</td></tr><tr><td>creation_date</td><td>Time when the block is created.</td></tr><tr><td>hash</td><td>Hash of the block, which represents a SHA256 hash represented in hex string for all the fields of the block concatenated together and separated with <code>:</code>. </td></tr><tr><td>miner_id</td><td>The ID of the miner generated the block.</td></tr><tr><td>round</td><td>Round when the block was generated.</td></tr><tr><td>round_random_seed</td><td>Seed number used to generate random numbers.</td></tr><tr><td>state_changes_count</td><td>Count of changes applied on the MPT state.</td></tr><tr><td>merkle_tree_root</td><td>Current root of the MPT computed from the transactions contained inside the block.</td></tr><tr><td>state_hash</td><td>Hex hash of the root of the MPT.</td></tr><tr><td>receipt_merkle_tree_root</td><td>The root of an MPT computed from the transactions  of the block.</td></tr><tr><td>num_txns</td><td>Number of the transactions in the block.</td></tr><tr><td>magic_block</td><td><a href="broken-reference">Magic Block</a> entity used while generating the block.</td></tr></tbody></table>

### Transaction

Transaction represents the format of communication between the clients and the smart contracts, securely and atomically, to execute an operation on their data. It also represents the unit of work and state change in the blockchain, and the main contents of the blocks. Transactions play an important role in any blockchain, by and large.

A transaction in the Züs Network consists of the following:

```go
type Transaction struct {
	// Hash of the transaction, SHA256 of the fields of the transaction, concatenated
	// together and represented in HEX format. It's calculated automatically so no need to
	// be provided in the response body for the endpoints using this entity.
	//
	// required: false
	Hash 		string 		`json:"hash"`
	
	// Version of the transaction. Useful to differentiate between recent transactions and old ones.
	// When a change occur in the schema of the transactions and deployed to the mainnet, we need to 
	// sure that the old transactions are still replayable. That's why we use versioning here
	// along with Hard Forking in the smartcontract code.
	//
	// required: true
	// default: "1.0"
	Version 	string 		`json:"version"`
	
	// ClientID of the client issuing the transaction
	//
	// required: true
	ClientID  string `json:"client_id"`

	// Public key of the client issuing the transaction
	//
	// required: true
	PublicKey string `json:"public_key,omitempty"`

	// ToClientID - the client id of the recipient, the other party in the transaction. It can be a client id or the address of a smart contract
	//
	// required: true
	ToClientID      string           `json:"to_client_id,omitempty"`

	// ChainID - the chain id of the transaction
	//
	// required: true
	ChainID         string           `json:"chain_id,omitempty"`

	// TransactionData - the data associated with the transaction
	//
	// required: true
	TransactionData string           `json:"transaction_data"`

	// Value - a numeric value associated with this transaction. Its role is determined by the smart contract function
	//
	// required: true
	Value           currency.Coin    `json:"transaction_value"`

	// Signature - Issuer signature of the transaction
	//
	// required: true
	Signature       string           `json:"signature"`
	
	// CreationDate - the time when the transaction was created
	//
	// required: true
	CreationDate    common.Timestamp `json:"creation_date"`

	// Fee - the fee associated with the transaction
	//
	// required: true
	Fee             currency.Coin    `json:"transaction_fee"`
	
	// Nonce - the nonce associated with the transaction
	//
	// required: true
	Nonce           int64            `json:"transaction_nonce"`

	// TransactionType - the type of the transaction. 
	//	Possible values are:
	//		- 0: TxnTypeSend - A transaction to send tokens to another account, state is maintained by account.
	//		- 10: TxnTypeData - A transaction to just store a piece of data on the block chain.
	//		- 1000: TxnTypeSmartContract - A smart contract transaction type.
	// required: true
	TransactionType   int    `json:"transaction_type"`

	// TransactionOutput - the output of the transaction
	//
	// required: true
	TransactionOutput string `json:"transaction_output,omitempty"`

	// OutputHash - the hash of the transaction output
	//
	// required: true
	OutputHash        string `json:"txn_output_hash"`

	// Status - the status of the transaction.
	//
	// TxnSuccess = 1 - Indicates the transaction is successful in updating the state or smart contract
	// TxnError   = 2 - Indicates a transaction has errors during execution
	// TxnFail    = 3 - Indicates a transaction has failed to update the state or smart contract
	//
	// required: true
	Status            int    `json:"transaction_status"`
}
```

### Transaction Confirmation

After the transaction is selected in a block and the block is finalized, the sharder fires an event to add transaction confirmation, which is then added to the EventDB. For a client to make sure their transaction was successful, or to check the error in case of failure, they need to query the confirmation from the [Sharder API](https://docs.zus.network/zus-docs/http-apis#sharder-node-api).

```go
type Confirmation struct {
	Version           string       `json:"version"`
	Hash              string       `json:"hash"`
	BlockHash         string       `json:"block_hash"`
	PreviousBlockHash string       `json:"previous_block_hash"`
	Transaction       *Transaction `json:"txn,omitempty"`
	datastore.CreationDateField
	MinerID               datastore.Key `json:"miner_id"`
	Round                 int64         `json:"round"`
	Status                int           `json:"transaction_status"`
	
	// low level fields
	RoundRandomSeed       int64         `json:"round_random_seed"`
	StateChangesCount     int           `json:"state_changes_count"`
	MerkleTreeRoot        string        `json:"merkle_tree_root"`
	MerkleTreePath        *util.MTPath  `json:"merkle_tree_path"`
	ReceiptMerkleTreeRoot string        `json:"receipt_merkle_tree_root"`
	ReceiptMerkleTreePath *util.MTPath  `json:"receipt_merkle_tree_path"`
}
```

<table><thead><tr><th width="236">Field</th><th>Description</th></tr></thead><tbody><tr><td>version</td><td>Default is "1.0". Reflects the used version of the schema.</td></tr><tr><td>hash</td><td>Hash of the transaction, acts as a unique identifier.</td></tr><tr><td>block_hash</td><td>Hash of the block, acts as a unique identifier.</td></tr><tr><td>previous_block_hash</td><td>Hash of the previous block, acts as a unique identifier.</td></tr><tr><td>txn</td><td><a href="#transaction">Transaction</a> entity of the transaction related to this confirmation.</td></tr><tr><td>miner_id</td><td>ID of the miner generated the block contained this transaction.</td></tr><tr><td>round</td><td>Round when the block contained this transaction was generated.</td></tr><tr><td>transaction_status</td><td>Status of the transaction. Same as in <a href="#transaction">Transaction Entity</a>.</td></tr><tr><td>round_random_seed</td><td>Random seed of the round contained this txn.</td></tr><tr><td>state_changes_count</td><td>Count of change in state associated with the block. Explained in <a href="broken-reference">Block Entity</a>.</td></tr><tr><td>merkle_tree_root</td><td>Current root of the merkle tree computed from the transactions contained inside the block.</td></tr><tr><td>merkle_tree_path</td><td>Path of the hash of the transaction in merkle tree of txns.</td></tr><tr><td>receipt_merkle_tree_root</td><td>The root of a merkle tree computed from the transaction hashes of the block.</td></tr><tr><td>receipt_merkle_tree_path</td><td>Path of the hash of the transaction in the merkle tree of txn receipts.</td></tr></tbody></table>

### Magic Block

Magic Block is an entity that contains meta information and configuration of the blockchain. It's changed during the view change process where it defines the new Active Set (set of miners/sharders contributing to the generation of the blocks in the blockchain) and the new hyper-parameter of the view change process (T, K, N).

```go
type MagicBlock struct {
	Hash 		       string		   `json:"hash"`
	PreviousMagicBlockHash string              `json:"previous_hash"`
	MagicBlockNumber       int64               `json:"magic_block_number"`
	StartingRound          int64               `json:"starting_round"`
	Miners                 *node.Pool          `json:"miners"`
	Sharders               *node.Pool          `json:"sharders"`
	ShareOrSigns           *GroupSharesOrSigns `json:"share_or_signs"`
	Mpks                   *Mpks               `json:"mpks"`
	T                      int                 `json:"t"`
	K                      int                 `json:"k"`
	N                      int                 `json:"n"`
}
```

<table><thead><tr><th width="236">Field</th><th>Description</th></tr></thead><tbody><tr><td>Hash</td><td>SHA256 Hash of the magic block fields concatenated with each other, in Hexadecimal format.</td></tr><tr><td>PreviousMagicBlockHash</td><td>The hash of the magic block previous to this magic block.</td></tr><tr><td>MagicBlockNumber</td><td>The order of this magic block.</td></tr><tr><td>StartingRound</td><td>Round where this magic block started to be used.</td></tr><tr><td>Miners</td><td>The set of the miners used in generating the blocks.</td></tr><tr><td>Sharders</td><td>The set of the sharders used in generating the blocks.</td></tr><tr><td>ShareOrSigns</td><td>Shares and signs are pieces of information used to build the active set during the phases of the view change process.</td></tr><tr><td>Mpks</td><td>Set of Miner Public Keys.</td></tr><tr><td>T</td><td>Threshold of signatures to verify a signature.</td></tr><tr><td>K</td><td>The threshold of signatures needed for the view change to be successful.</td></tr><tr><td>N</td><td>The maximum number of miners, n.</td></tr></tbody></table>