It makes much more sense this way:

LedgerEngine: Performs high-level ledger operations.
TransactionEngine: Performs high-level transaction operations.

src/LedgerEngine.h

@@ -0,0 +1,45 @@
+#ifndef __LEDGERENGINE__
+#define __LEDGERENGINE__
+
+#include <cstring>
+
+#include <boost/shared_ptr.hpp>
+
+#include "uint256.h"
+#include "Ledger.h"
+#include "Currency.h"
+#include "SerializedLedger.h"
+
+// A LedgerEngine handles high-level operations to a ledger
+
+enum LedgerEngineParms
+{
+	lepCREATE = 1,	// Create if not present
+};
+
+class LedgerEngine
+{
+public:
+	typedef boost::shared_ptr<LedgerEngine> pointer;
+
+protected:
+	Ledger::pointer mLedger;
+
+public:
+	LedgerEngine() { ; }
+	LedgerEngine(Ledger::pointer l) : mLedger(l) { ; }
+
+	Ledger::pointer getTargetLedger() { return mLedger; }
+	void setTargetLedger(Ledger::pointer ledger) { mLedger = ledger; }
+
+	SerializedLedgerEntry::pointer getAccountRoot(LedgerEngineParms parms, const uint160& accountID);
+
+	SerializedLedgerEntry::pointer getNickname(LedgerEngineParms parms, const std::string& nickname);
+	SerializedLedgerEntry::pointer getNickname(LedgerEngineParms parms, const uint256& nickHash);
+
+	SerializedLedgerEntry::pointer getRippleState(LedgerEngineParms parms, const uint160& offeror,
+		const uint160& borrower, const Currency& currency);
+
+};
+
+#endif

src/TransactionEngine.h

@@ -2,6 +2,8 @@
 #define __TRANSACTIONENGINE__
 
 #include "Ledger.h"
+#include "LedgerEngine.h"
+#include "Currency.h"
 #include "SerializedTransaction.h"
 #include "SerializedLedger.h"
 
@@ -32,7 +34,7 @@ enum TransactionEngineParams
 class TransactionEngine
 {
 protected:
-	Ledger::pointer mTargetLedger;
+	LedgerEngine::pointer mTxnEngine;
 
 	TransactionEngineResult doPayment(const SerializedTransaction&, SerializedLedgerEntry& source);
 	TransactionEngineResult doInvoice(const SerializedTransaction&, SerializedLedgerEntry& source);
@@ -43,10 +45,11 @@ protected:
 	TransactionEngineResult doDelete(const SerializedTransaction&, SerializedLedgerEntry& source);
 
 public:
-	TransactionEngine(Ledger::pointer targetLedger) : mTargetLedger(targetLedger) { ; }
+	TransactionEngine() { ; }
+	TransactionEngine(LedgerEngine::pointer txnEngine) : mTxnEngine(txnEngine) { ; }
 
-	Ledger::pointer getTargetLedger() { return mTargetLedger; }
+	LedgerEngine::pointer getLedgerEngine() { return mTxnEngine; }
-	void setTargetLedger(Ledger::pointer targetLedger) { mTargetLedger = targetLedger; }
+	void setLedgerEngine(LedgerEngine::pointer engine) { mTxnEngine = engine; }
 
 	TransactionEngineResult applyTransaction(const SerializedTransaction&, TransactionEngineParams);
 };