Abstract: Program visualization supports program comprehension by providing software properties in visualized forms. We introduce and analyze current representative visualization tools from the viewpoint of effective visualization of semantic properties for large-scale software. Then, we present the design and implementation of our visualization tool that helps users understand the relationship among modules of a program at various levels from program statements to packages. The tool has several features to overcome visual complexities of large software such as limitation of displayed nodes and auxiliary table. The tool stores underlying data structures in a graph database and handles concurrency and scalability effectively. We also explain the implementation of our tool and provide experimental results.