There has been a growing need for querying heterogeneous data sources, namely XML and Relational databases. Since the relational model is the most data model used to manage data for years. Similarly, the eXtensible Markup Language (XML) is quickly emerging as the de facto standard for data exchange over the Internet. Hence, bridging these two models is surely need. Furthermore, each database system uses a particular query language to manipulate data. So, users need to know each query language of each data model. To this point, we aim to define a system to retrieve data regardless of the nature of the model used and eliminates the burden of learning new languages. In such way, the existing users' knowledge about a query language will be enough and will meet the purpose. Thus, this paper addresses the problem of accessing both XML and relational data, by using a unique query language expressed with whether SQL or XPath. We rely on a new approach in the translation process to convert the user query into the suitable query language according to the nature of the data interrogated.

There has been significant recent interest in data integration and querying heterogeneous data sources. Thus, in our work, we aim to develop a system for querying databases regardless of the nature of their model, especially XML and relational data model as they are increasingly related in practice, Due to that we choose to make them the first models under study in this contribution. In fact, the relational model is the most dominated data model in most organizations, and it has utility widely used to manage and maintain a large volume of data. At the same time, XML is increasingly becoming the lingua franca of data interchange and has received considerable attention due to its multiple benefits. Besides, each one of these models has its specific query languages, and it will be important to ensure a flexible way to access information represented by both technologies. Thus, this paper addresses the problem of accessing data independently of the model used, by using a unique query language. Since users and even developers may not be familiar with multiple query language syntax at a time, we need to facilitate accessing data by making one single query in any query language enough to retrieve data from any data model.