bool createString(const char* context, const char* key, const char* value, time_t expiration);
int readString(const char* context, const char* key, string* pvalue=nullptr, time_t* pexpiration=nullptr, int version=0);
int updateString(const char* context, const char* key, const char* value=nullptr, time_t expiration=0, int version=0);
bool createString(const char* context, const char* key, const char* value, time_t expiration);
int readString(const char* context, const char* key, string* pvalue=nullptr, time_t* pexpiration=nullptr, int version=0);
int updateString(const char* context, const char* key, const char* value=nullptr, time_t expiration=0, int version=0);