然而，虚表也存在一些缺点。
现在，我们要访问的虚表的第二个成员。
这里一半的马只是徒有虚表。
该功能建立在IDS提供的虚表接口（VTI）之上。
This functionality is built upon the virtual table interface (VTI) provided by IDS.
虚表还可以用于装载TimeSeries数据。
Virtual tables can also be used for loading TimeSeries data.
然而，在创建虚表(或视图)之前，应用服务器不能使用表。
However, the tables are not ready to be used by the application server until virtual tables (or Views) have been created.
另一个限制是，不能在TimeSeries虚表上创建索引。
Another limitation is that you cannot create indexes on TimeSeries virtual tables. Listing 11 shows how to build virtual tables for the baseball example.
注意，这个例子为每个timeseries列创建一个单独的虚表。
Notice that the example creates a separate virtual table for each TimeSeries column.
有一个为每个类的虚表，其中包含每个成员的功能的实现的指针列表。
There's a virtual table for each class, which contains a list of Pointers to the implementation of each member function.
在虚表的名称后面，我添加一个“ _ virt ”，这样就可以知道它是一个虚表。
I add "_virt" to the end of the virtual table's name, so that I know it is a virtual table.
在我的测试中，虚表上的查询比做同样查询的TimeSeries函数要慢一个数量级。
In my tests, it can be an order of magnitude slower than a TimeSeries function that does the same query.
而且，虚表查询偶尔还会返回奇怪的结果，而在使用TimeSeries函数时不会碰到这种情况。
Also, I have occasionally encountered strange results from virtual table queries that do not occur when I use the direct TimeSeries functions.
看过了TimeSeries函数和强制类型转换以及其他元素之后，虚表看上去是一种自然的选择。
After seeing the TimeSeries functions and casts and other elements, a virtual table looks like an easy choice.
虚表上的查询可能非常慢，尤其是在where子句中使用某个TimeSeries元素时更是如此。
It can be very slow to do queries across a virtual table, especially if you use one of the TimeSeries elements in the WHERE clause.
每个对象都有一些附加字节，通用语言运行库用来管理对象，如对象的虚表指针和同步锁定引用。
Every object has some additional bytes that the common language runtime USES to manage the object, such as the object's virtual table pointer and a reference to a sync block.
虚表在快速查询、装载数据和用于报告编写程序及其他终端用户工具等方面很出色（如果性能尚能接受的话）。
Virtual tables are great for quick queries, loading data, and for use in report writers and other end-user tools (if the performance doesn't kill you).
TimeSeriesDataBlade提供另一种工具来降低处理 TimeSeries数据的复杂性 —— 这就是用于构建虚表的例程。
The TimeSeries DataBlade provides another tool to cut through some of the complexity of working with TimeSeries data -- routines to build virtual tables.
Rhino代码读起来很像C程序：它避免过多的分配，并且尽量多地使用跳转表（Jump Tables）来避免虚方法查询（Virtual Method Lookups）的额外开支。
The Rhino code base reads almost like C code: it avoids allocation and does as much as possible with jump tables to avoid the overhead of virtual method lookups.
基于对称分量法，对电能表中性点虚接后的电压互感器二次压降进行了分析，得出了正确接线前后的计量误差变化量。
The on-site test results indicate that energy meter's neutral point virtual connection has a great effect on PT secondary voltage drop.
基于对称分量法，对电能表中性点虚接后的电压互感器二次压降进行了分析，得出了正确接线前后的计量误差变化量。
The on-site test results indicate that energy meter's neutral point virtual connection has a great effect on PT secondary voltage drop.
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