We introduce a model of uncertainty where documents are not uniquely identified in a reference network, and some links may be incorrect. It generalizes the probabilistic approach on databases to graphs, and defines subgraphs with a probability distribution. The answer to a relational query is a distribution of documents, and we study how to approximate the ranking of the most likely documents and quantify the quality of the approximation. The answer to a function query is a distribution of values and we consider the size of the interval of Minimum and Maximum values as a measure for the precision of the answer.