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+* Command Family
+* Start Date: YYYY-MM-DD
+* RFC PR: (leave this empty)
+* Transact Issue: (leave this empty)
+
+# Summary
+[summary]: #summary
+
+The Command Family is a transaction family that can exercise all of the
+operations provided on the TransactionContext in addition to other actions, such
+as sleeping or marking the transaction as invalid.  This family will be used for
+creating a wide variety of tests, both for correctness and performance of the
+Transact library.
+
+# Motivation
+[motivation]: #motivation
+
+This family will be used for creating a wide variety of tests, both for
+correctness and performance.
+
+# Guide-level explanation
+[guide-level-explanation]: #guide-level-explanation
+
+The Command family is a Transact transaction family that provides the following
+operations, based on operations defined in its transaction payloads.  These
+operations, or commands, cover the following actions:
+
+* Read state entries
+* Write state entries
+* Add an event to the receipt
+* Add arbitrary receipt data
+* "Return" InvalidTransaction
+* "Return" InternalError
+* Sleep for a specified duration
+
+The above operations provide test coverage of all the possible behaviours of a
+transaction handler.
+
+Additionally, a Command Family workload tool will be provided to generate a
+stream of command family transactions.  The transactions themselves will be
+described by a yaml file declaration.  The tool will accept arguments to adjust
+the rates, domain of arguments and random seed of a given workload run.
+
+# Reference-level explanation
+[reference-level-explanation]: #reference-level-explanation
+
+## Transaction Payload
+
+The transaction payload for the command family will be as follows:
+
+```protobuf
+// A transaction payload for the Command Family
+message CommandPayload {
+    // The list of commands to execute
+    repeated Command commands = 1;
+}
+
+// A key-value pair where the value is a bytes field.
+message BytesEntry {
+    // The key, for instance a state address or a string value, depending on
+    // the target of the entry.
+    string key = 1;
+    // The byte value to be stored
+    bytes value = 2;
+}
+
+// The list of state keys to be retrieved via a GET_STATE command.
+message GetState {
+    // a non-empty list of valid state keys
+    repeated string state_keys = 1;
+}
+
+// The list of state entries to be set via a SET_STATE command.
+message SetState {
+    // a non-empty list of BytesEntry instances, where the key field is a
+    // valid state key.
+    repeated BytesEntry state_writes = 1;
+}
+
+// The list of state keys to be deleted via a DELETE_STATE command.
+message DeleteState {
+    // a non-empty list of valid state keys
+    repeated string state_keys = 1;
+}
+
+// Describes an event to add to the receipt via an ADD_EVENT command.
+message AddEvent {
+    // The event type
+    string type = 1;
+    // The attribute entries
+    repeated BytesEntry attributes = 2;
+    // Arbitrary opaque event data
+    bytes data = 3;
+}
+
+// The opaque byte data to add to the receipt via an ADD_RECEIPT_DATA
+// command. 
+message AddReceiptData {
+    // a non-empty byte array
+    bytes receipt_data = 1;
+}
+
+// The duration and method of sleep to apply during a SLEEP command.
+message Sleep {
+    enum SleepType {
+        // This will wait, releasing cpu utilization to other processes 
+        WAIT = 0;
+        // This will consume a cpu core for the specified time
+        BUSY_WAIT = 1;
+    }
+
+    // The duration to sleep, in milliseconds
+    u32 duration_millis = 1;
+    SleepType sleep_type = 2;
+}
+
+// The details to return on an RETURN_INVALID command.
+message ReturnInvalid {
+    // An optional error message
+    string error_message = 1;
+}
+
+// The details to return on an RETURN_INTERNAL_ERROR command.
+message ReturnInternalError {
+    // An optional error message
+    string error_message = 1;
+}
+
+// A command to be executed
+message Command {
+    enum CommandType {
+        UNSET_COMMAND_TYPE = 0;
+        GET_STATE = 1;
+        SET_STATE = 2;
+        DELETE_STATE = 3;
+        ADD_EVENT = 4;
+        ADD_RECEIPT_DATA = 5;
+        SLEEP = 6;
+        RETURN_INVALID = 7;
+        RETURN_INTERNAL_ERROR = 8;
+    }
+
+    // The type of the command, which indicates which of the following 
+    // fields will be set.
+    CommandType type = 1;
+
+    GetState get_state = 2;
+    SetState set_state = 3;
+    DeleteState delete_state = 4;
+    AddEvent add_event = 5;
+    AddReceiptData add_receipt_data = 6;
+    Sleep sleep = 7;
+    ReturnInvalid return_invalid = 8;
+    ReturnInternalError return_internal_error = 9;
+}
+```
+
+## Command Execution
+
+A Command Family transaction consists of an ordered list of Commands. The
+commands are executed in order and only if the preceding command was successful.
+Commands which return an explicit result (invalid or internal error) will
+short-circuit the remaining commands in the list.
+
+Each command performs a single operation, from the perspective of
+TransactionContext, or from the result returned.  The sleep command is currently
+an exception, in that the transaction handler will pause for the specified
+duration before proceeding to the next command, if any.
+
+### Get State
+
+The `GET_STATE` command will use the `state_keys` field of the `GetState`
+message to request a read of the addresses specified.  This will make use of the
+`TransactionContext`'s `get_state_entries` method. In other words, it will only
+make a single call to the context. 
+
+Each entry in the `state_keys` field must be a valid state key (for example, a
+valid address in a Sawtooth merkle trie). 
+
+Note, no validation will occur if the requested state value is actually
+returned, nor what the entry should or shouldn't contain.
+
+### Set State
+
+The `SET_STATE` command will use the `state_writes` field of the `SetState`
+message to request a write of the bytes entries specified.  This will make use
+of the `TransactionContext`'s `set_state_entries` method, where the keys and
+values are specified by `BytesEntry` messages. In other words, it will only make
+a single call to the context.
+
+The key in the `BytesEntry` must be a valid state key (for example, a valid
+address in a Sawtooth merkle trie). 
+
+### Delete State
+
+The `DELETE_STATE` command will use the `state_keys` field of the `DeleteState`
+message to request a read of the addresses specified.  This will make use of the
+`TransactionContext`'s `delete_state_entries` method. In other words, it will
+only make a single call to the context. 
+
+Each entry in the `state_keys` field must be a valid state key (for example, a
+valid address in a Sawtooth merkle trie). 
+
+### Add Event
+
+The `ADD_EVENT` command will use the event field of the `AddEvent` message to
+add an event to the transaction receipt.  This will make use of the
+`TransactionContext`'s `add_event` method, using the contents of the `Event`
+message contained in the event field to set the matching parameters.
+
+The Event type field must not be empty. The remaining fields, attributes and
+data, may be empty.
+
+### Add Receipt Data
+
+The `ADD_RECEIPT_DATA` command will use the `receipt_data` field of the
+`AddReceiptData` message to add this data to the transaction receipt.  This will
+make use of the `TransactionContext`'s `add_receipt_data` method.
+
+The `receipt_data` field must not be empty.
+
+### Sleep
+
+The `SLEEP` command will use the `duration_millis` field of the `Sleep` message
+in order to delay the execution of the transaction.  This field is a millisecond
+value.  The `SleepType` indicates whether the transaction handler should
+busy-wait (i.e. consume CPU resources) or standard wait.
+
+The provided sleep duration must not be zero.
+
+### Return Invalid Transaction
+
+The `RETURN_INVALID` command will force the return of an `InvalidTransaction`
+result from the transaction handler.  It will use the `error_message` field in
+the ReturnInvalid message to provide arbitrary feedback. Any remaining commands
+will be ignored.
+
+The `error_message` field may be empty.
+
+### Return Internal Error
+
+The `RETURN_INTERNAL_ERROR` command will force the return of an `InternalError`
+result from the transaction handler.  It will use the `error_message` field in
+the `ReturnInternalError` message to provide arbitrary feedback. Any remaining
+commands will be ignored.
+
+The `error_message` field may be empty.
+
+## Transaction Header
+
+The transaction header is a standard header in that it will include the family
+name and the family version as normal.
+
+family_name: "command"
+family_version: "0.1"
+
+In a Sawtooth context, there is an additional field for namespaces. For the
+command family, the namespace should be "any" (i.e. `*`).  The command family
+should be allowed to read and write any value from/to state.  
+
+Alternatively, the namespace should be set to the first 6 char of the SHA-512
+hash of the family name, "command".  Address values used in `GET`-, `SET`- or
+`DELETE_STATE` commands would have to be required to be under that namespace.
+
+## Workload Generator
+
+The workload generator for the command family will generate a stream of batches,
+consisting of one or more command transactions.  These transactions generated by
+the stream will be described declaratively using a yaml file.
+
+The declarations should describe the commands to be used, with ranges of values
+that may be generated.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+None.
+
+# Rationale and alternatives
+[alternatives]: #alternatives
+
+This family is designed to improve the overall testing of the Transact library.
+It provides coverage of the operations available to a transaction handler and
+therefore improves overall testing of the Transact library.
+
+Alternatively, individual transaction families could be created for specific
+test circumstances, using the transaction order as a way to implement operation
+order.  This approach has the side-effect of operations potentially occurring in
+an unpredictable order, depending on the scheduler implementation.  Likewise, it
+would not allow for testing multiple operations before failing the transaction.
+
+# Prior art
+[prior-art]: #prior-art
+
+The Command family builds on existing Sawtooth example and test-related
+transaction families, such as IntKey and Smallbank.  Both of these exercise
+subsets of the operations on the TransactionContext, but not in a broad sense.
+Likewise, the workload generation for these families is mainly focused on batch
+throughput, and not focused tests on the effects of certain operations.
+
+# Unresolved questions
+[unresolved]: #unresolved-questions
+
+None.