如上图所示，CDXLOperator作为Base class for operators in a DXL tree，其子类CDXLLogical、CDXLScalar、CDXLPhysical作为逻辑节点、物理节点和Scalar节点的DXL表示类，因此其包含了这些类的共同部分特性，比如获取其DXL节点表示的函数GetDXLOperator、获取其Operator类型的函数GetDXLOperatorType，如下图右侧所示。

class CDXLOperator : public CRefCount {
private:	
	CDXLOperator(const CDXLOperator &); // private copy constructor
protected:	
	CMemoryPool *m_mp; // memory pool
public:	
	explicit CDXLOperator(CMemoryPool *); // ctor/dtor
	virtual ~CDXLOperator();	
	virtual Edxlopid GetDXLOperator() const = 0; // ident accessors	
	virtual const CWStringConst *GetOpNameStr() const = 0; // name of the operator
	virtual Edxloptype GetDXLOperatorType() const = 0;

	// serialize operator in DXL format given a serializer object and the
	// host DXL node, providing access to the operator's children
	virtual void SerializeToDXL(CXMLSerializer *, const CDXLNode *) const = 0;

	// check if given column is defined by operator
	virtual BOOL IsColDefined(ULONG	 // colid ) const { // by default, operator does not define columns
		return false;
	}

	static const CWStringConst *GetJoinTypeNameStr(EdxlJoinType);	
	static const CWStringConst *GetIdxScanDirectionStr(EdxlIndexScanDirection); // Return the index scan direction
};

其中最重要的函数是SerializeToDXL，该函数用于使用给定serializer object将operator序列化成DXL format。而GetOpNameStr函数则是获取该operator DXL类在DXL format中的标签，其实就是xml中的标签，如下代码所示，CDXLScalarAggref的标签为CDXLTokens::GetDXLTokenStr(EdxltokenScalarAggref)，即为AggFunc。

const CWStringConst *CDXLScalarAggref::GetOpNameStr() const{
	return CDXLTokens::GetDXLTokenStr(EdxltokenScalarAggref);
}
		{EdxltokenScalarAggref, GPOS_WSZ_LIT("AggFunc")},

operators in a DXL tree仅仅是DXL tree中的一部分，除了Operator DXL节点的标签，还有其他标签，比如Comment、Plan、Id等。