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Mastering Data Warehouse DesignRelational and Dimensional Techniques phần 7

Cung cấp một lịch để đo số lượng ngày công lao động giữa Kiên Hai sự kiện, như vậy là các Bắt đầu và kết thúc của một thời kỳ khuyến mãi, và cho truy cập dữ liệu Tạo điều kiện cho một số lượng bằng nhau Bất kể ngày công lao động trong những ngày trôi qua. Tiền đề lịch phía sau nhà máy để homogenize dòng thời gian để tính toán đó WS ngày | Modeling Transactions 257 Delta Snapshot Interface The delta snapshot is a commonly used interface for reference data such as a customer master list. The basic delta snapshot would contain a row or transaction that changed since the last extraction. It would contain the current state of all attributes without information about what in particular had changed. This is the easiest of the delta interfaces to process in most cases. Since it contains both changed and unchanged attributes creating time-variant snapshots does not require retrieval of the previous version of the row. It also does not require the process to examine each column to determine change but rather only those columns where such an examination is necessary. And when such examination is necessary there are a number of techniques discussed later in this chapter that allow it to occur efficiently with minimal development effort. Transaction Interface A transaction interface is special form of delta snapshot interface. A transaction interface is made up of three parts an action that is to be performed data that identifies the subject and data that defines the magnitude of the change. Atrans-action interface is always complete and received once. This latter characteristic differentiates it from a delta snapshot. In a delta snapshot the same instance may be received repeatedly over time as it is updated. Instances in a transaction interface are never updated. The term should not be confused with a business transaction. While the characteristics are basically the same the term as it is used here describes the interaction between systems. You may have an interface that provides business transactions but such an interface may be in the form of a delta snapshot or a transaction interface. The ways that each interface is processed are significantly different. Database Transaction Logs Database transaction logs are another form of delta interface. They are discussed separately because the delta capture occurs .