A sales transaction is a transaction between a seller and a buyer in a business followed by the process of delivering a product in the form of goods or services. In the business world, the sales process is the key to success for a business person. Because the existing data will accumulate every time there is a transaction so that the existing data has not been used properly by decision makers. This study aims to provide a report on research results regarding the application of the a priori algorithm to determine the sales pattern of interest. This research is supported by a software development methodology called the Software Development Life Cycle (SDLC) Waterfall method. In the process carried out in the implementation of this software there are several steps such as problem determination, identification and resolution of risks, development and testing. Each step at this stage is used to map the existing problems until the formation of an application as needed. As a result of this research is an application based on an a priori algorithm consisting of Itemset selection and association rules. The output of this software is used for reference data on stock of goods as well as optimizing the calculation of sales pattern analysis of products of interest.

Keywords: Sales Transaction, Apriori Algorithm, Association Rules, Waterfall