The different activities related to debugging such as program instrumentation, representation of execution trace and analysis of trace are not typically performed in an unified framework. We propose \textit{BOLD}, an Ontology-based Log Debugger to unify and standardize the activities in debugging. The syntactical information of programs can be represented in the from of Resource Description Framework (RDF) triples. Using the BOLD framework, the programs can be automatically instrumented by using declarative specifications over these triples. A salient feature of the framework is to store the execution trace of the program also as RDF triples called \textit{trace triples}. These triples can be queried to implement the common debug operations. The novelty of the framework is to abstract these triples as \textit{spans} for high-level reasoning. A span gives a way of examining the values of a particular variable over certain portion of the program execution. The properties of the spans are defined formally as a Web Ontology Language (OWL) ontology called \textit{Program Debug (PD) Ontology}. Using the span abstraction and PD ontology, end-users can debug a given buggy program in a standard manner. A notable feature of using ontology is that users can accurately debug in some cases of missing information, which can be practically useful. To demonstrate the feasibility of the proposed framework, we have debugged the programs in a standard bug benchmark suite Software-artifact Infrastructure Repository (SIR). Experiments show that the querying time is almost the same as in \texttt{gdb}. The reasoning time depends on the sub-language of OWL. We find that the expressibility offered by OWL-DL language is sufficient for the bugs in SIR programs; but to achieve scalability in reasoning, a restricted OWL-RL language is required.