某商业集团数据库中有两个实体集。一是“商店”实体集，属性有商店编号、商店名、地址、电话等；另一是“职工”实体集，属性有职工编号、姓名、性别、年龄等。职工商店间存在着工作关系。一个商店有若干职工，每个职工只能在一个商店工作。职工在商店工作有一个进店日期、月薪等属性。 (1) 试画出E-R图。 (2) 将E-R图转换成关系模型，并注明每个表的主码和外码。
参考答案：
解析：(1) E-R图如下图所示。 (2) 转换成关系模型有两个表： 商店(商店编号，商店名，地址，电话) 职工(职工编号，姓名，性别，年龄，，进店日期．月薪)
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| My son Joey was born with club feet. The doctors said that with treatment he would be able to walk, but would never run very well. The first three years of his life was 1 in hospital. By the time he was eight, you wouldn't know he has a problem when you saw him 2 . Children in our neighborhood always ran around 3 their play, and Joey would jump and ran and play, 4 . We never told him that he probably wouldn't be 5 to run like the other children. So he didn't know. In 6 grade he decided to join the school running team. Every day he trained. He ran more than any of the others, 7 only the top seven runners would be chosen to run for the 8 . We didn't tell him he probably would never make the team, so he didn't know. He ran four to five mile every day-even when he had a fever. I was 9 , so I went to 10 him after school. I found him running 11 . I asked him how he felt."Okay," he said. He has two more miles to go. Yet he looked straight ahead and kept 12 . Two weeks later, the names of the team 13 were caked. Joey was number six on the list. Joey had 14 the team. He was in seventh grade - the other six team members were all eighth graders. We never told him he couldn't do it … so he didn't know. He just 15 it. | ||||
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（2） 此木块的重力是多少？