This paper addresses the challenge of indexing and querying XML data efficiently, particularly for regular path expressions. The authors propose a new system called XISS, which uses a numbering scheme for elements and attributes to quickly determine the ancestor-descendant relationships in XML data. The system includes three main index structures: element index, attribute index, and structure index. They also introduce three algorithms for processing regular path expressions: $\mathcal{E}\mathcal{E}$-Join for searching paths between elements, $\mathcal{E}\mathcal{A}$-Join for scanning sorted elements and attributes, and $\mathcal{K}\mathcal{C}$-Join for finding Kleene-Closure on repeated paths or elements. Experimental results show that the proposed algorithms can process XML queries up to 10 times faster than conventional approaches. The paper discusses the decomposition of regular path expressions and the effectiveness of the proposed algorithms in handling various query scenarios.This paper addresses the challenge of indexing and querying XML data efficiently, particularly for regular path expressions. The authors propose a new system called XISS, which uses a numbering scheme for elements and attributes to quickly determine the ancestor-descendant relationships in XML data. The system includes three main index structures: element index, attribute index, and structure index. They also introduce three algorithms for processing regular path expressions: $\mathcal{E}\mathcal{E}$-Join for searching paths between elements, $\mathcal{E}\mathcal{A}$-Join for scanning sorted elements and attributes, and $\mathcal{K}\mathcal{C}$-Join for finding Kleene-Closure on repeated paths or elements. Experimental results show that the proposed algorithms can process XML queries up to 10 times faster than conventional approaches. The paper discusses the decomposition of regular path expressions and the effectiveness of the proposed algorithms in handling various query scenarios.