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In z/OS, it is possible to catalog successive updates or generations of related data. They are called generation data groups (GDGs).

在z/OS里可以编目继承性的更新或相关数据的世代，他们叫做“世代”数据组。

Each data set within a GDG is called a generation or generation data set (GDS). A generation data group (GDG) is a collection of historically related non-VSAM data sets that are arranged in chronological order. That is, each data set is historically related to the others in the group.

每一个GDG中的数据集叫做一个世代数据集。一个GDG是一组有历史关联的非VSAM数据集按照年代顺序排列组成的，即每个数据集是于组中其他数据集历史关联的。

Within a GDG, the generations can have like or unlike DCB attributes and data set organizations. If the attributes and organizations of all generations in a group are identical, the generations can be retrieved together as a single data set.

在GDG中，数据集可以使用相同的或不同的DCB属性和数据结构。如果一个组中数据集的这些属性和结构都是一样的，那么这个世代可以作为一个单独的数据集来访问。

There are advantages to grouping related data sets. For example:
All of the data sets in the group can be referred to by a common name.
The operating system is able to keep the generations in chronological order.
Outdated or obsolete generations can be automatically deleted by the operating system.

把相关联的数据集组合起来有下列好处：
组中所有数据集可以共用一个名字；
OS可以保证世代依年代顺序；
过期的或者作废的数据集可以被系统自动删除。

Generation data sets have sequentially ordered absolute and relative names that represent their age. The operating system’s catalog management routines use the absolute generation name. Older data sets have smaller absolute numbers. The relative name is a signed integer used to refer to the latest (0), the next to the latest (-1), and so forth, generation.

GDG用绝对顺序的排列和相对名来体现他们的年代。OS的常规编目管理用绝对的世代名称。旧的数据集用小一些的绝对数，相对名是一个带符号整数用来体现：最新的（0），次新的（－1）等等。

For example, the data set name LAB.PAYROLL(0) refers to the most recent data set of the group; LAB.PAYROLL(-1) refers to the second most recent data set; and so forth. The relative number can also be used to catalog a new generation (+1). A generation data group (GDG) base is allocated in a catalog before the generation data sets are cataloged. Each GDG is represented by a GDG base entry.

比如，数据集LAB.PAYROLL(0)表示为组中最新的数据集；LAB.PAYROLL(-1)表示是第二新的。相对数同样可以用来建立一个新的世代（＋1）。一个GDG base建立在GDGs建立之前，每个GDG都是由GDG base 条目来显示的。