Describes each data element within the bulk data store, such as source organization, application support, data summary, index, catalog, or digests.
描述批量数据存储中的每个数据元素，例如源组织、应用程序支持、数据汇总、索引、目录或摘要。
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Simple properties of items can be primitive data types, such as integers and strings, or a special data type called content, which is used to storebulk data such as the bytes of a file.