  Smart contracts are pivotal for implementing various functions due to their
interactivity with external data. However, this interactivity also presents
challenges in terms of security and reliability. There is a lack of statistical
and quantitative research on the interaction between smart contracts and
external data. To fill this gap, we thoroughly examine 10,500 actual smart
contracts to select 9,356 valid samples, excluding those that are outdated or
have compilation errors. Utilizing code parsing techniques, the study
transformed contract code into Abstract Syntax Trees (ASTs) and extracted
keywords related to external data dependency through code analysis. By
comparing the ASTs with the keyword list, we conduct a quantitative analysis of
the number and proportion of contracts involving external data interaction.
Furthermore, we collect over 3,600 security audit reports and manually filter
249 (approximately 9%) reports related to external data interaction,
categorizing the external data dependency in these contracts. We also explore
the relationship between the complexity of smart contracts and their dependence
on external data.
