blocks|key|2744650|text|弱实体是只有在被另一个实体拥有时才能存在的实体。例如:房间只能存在于建筑物中。另一方面，轮胎可能被认为是一个强大的实体，因为它也可以在不连接到汽车的情况下存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2744651|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

A weak entity is one that can only exist when owned by another one. 
For example: a ROOM can only exist in a BUILDING. On the other hand, a TIRE might be considered as a strong entity because it also can exist without being attached to a CAR.

blocks|key|2744658|text|只是玩弄它，问题是强实体类型，答案是弱的。问题总是存在的，但答案需要存在一个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2744659|示例：Don't+ask+'Why?'+if+Your+Dad's+a+Chemistry+Professor|offset|length|2744660|entityMap|0|LINK|mutability|MUTABLE|url|http://nigeriavillagesquare.com/forum/lounge/11704-dont-ask-why-if-your-dads-chemistry-professor.html^0|0|3|1G|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Just to play with it, question is strong entity type and answer is weak. Question is always there, but an answer requires a question to exist.

Example: <a href="http://nigeriavillagesquare.com/forum/lounge/11704-dont-ask-why-if-your-dads-chemistry-professor.html" rel="noreferrer">Don't ask 'Why?' if Your Dad's a Chemistry Professor</a>

blocks|key|51689|text|弱实体是指不能通过自身属性完全识别的实体，它联合使用外键作为属性(一般取与之相关的实体的主键)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|51690|示例|51691|房间的存在完全依赖于酒店的存在。因此，房间可以看作是酒店的弱实体。|51692|另一个例子是|51693|如果某个银行不再存在，那么该银行的银行账户就不存在。|51694|entityMap^0|0|3|0|0|2|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|W|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|X|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|O|$]]

A weak entity is the entity which can't be fully identified by its own attributes and takes the foreign key as an attribute (generally it takes the primary key of the entity it is related to) in conjunction.

Examples

The existence of rooms is entirely dependent on the existence of a hotel. So room can be seen as the weak entity of the hotel. 
Another example is the 
bank account of a particular bank has no existence if the bank doesn't exist anymore.

blocks|key|2535098|text|公司保险单为雇员和任何受扶养人提供保险，受扶养人在没有雇员的情况下不能存在；也就是说，一个人不能作为受扶养人获得保险，除非该人是employee.DEPENDENT的受扶养人是关系中的弱实体“雇员有受扶养人”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2535099|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

A company insurance policy insures an employee and any dependents, the DEPENDENT cannot exist without the EMPLOYEE; that is, a person cannot get insurance coverage as a dependent unless the person is a dependent of an employee.DEPENDENT is the weak entity in the relationship "EMPLOYEE has DEPENDENT"

blocks|key|2535386|text|强实体|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2535387|它可以在没有任何其他实体的情况下存在。|2535388|示例|offset|length|style|BOLD|2535389|Customer(customerid,+name,+surname)|code-block|syntax|javascript|2535390|弱实体|2535391|它依赖于一个占主导地位的实体，没有一个强大的实体它就不能存在。|2535392|2535393|Adress(addressid,+adressName,+customerid)|2535394|entityMap^0|0|0|0|2|0|0|0|0|0|2|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Z|8|@$F|10|G|11|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|12|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|13|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|14|8|@]|9|@]|A|$]]|$1|S|3|E|5|6|7|15|8|@$F|16|G|17|H|I]]|9|@]|A|$]]|$1|T|3|U|5|L|7|18|8|@]|9|@]|A|$M|N]]|$1|V|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|W|$]]

<h2>Strong entity</h2>

It can exist without any other entity.

Example

<pre><code>Customer(customerid, name, surname)
</code></pre>

<h2>Weak entity</h2>

It depends on a dominant entity, and it cannot exist without a strong entity.

Example

<pre><code>Adress(addressid, adressName, customerid)
</code></pre>

blocks|key|52782|text|弱实体的存在是为了解决多值属性问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|52783|有两种类型的多值属性。一种是简单的对象的许多值，例如“爱好”作为学生的属性。学生可以有许多不同的爱好。如果我们把兴趣放在学生实体集中，那么“爱好”就不再是唯一的了。我们创建一个单独的实体集作为业余爱好。然后，我们根据需要将业余爱好和学生联系起来。爱好实体集现在是关联实体集。至于它是否弱，我们需要检查每个实体是否有足够的唯一标识符来识别它。在许多人看来，一个爱好的名字就足以识别它。|52784|另一种类型的多值属性问题确实需要弱实体来修复它。让我们假设在食品杂货库存系统中设置了一个项目实体。项目是类别项目还是实际项目？这是一个重要的问题，因为客户可以一次以一定的数量购买相同的商品，但他也可以在不同的时间以不同的数量购买相同的商品。你能看到相同的物品但不同的物体吗？该项目现在是一个多值属性。我们首先通过将类别项与实际项分开来解决它。这两者现在是不同的实体集。类别项目具有项目的描述性属性，就像您通常想到的项目一样。实际的项目不能再有描述性属性，因为我们不能有冗余的问题。实际项目只能有项目的日期、时间和金额。您可以根据需要链接它们。现在，让我们讨论一下其中一个是否是另一个的弱实体。描述性属性足以标识类别项实体集中的每个实体。实际项目只有日期、时间和金额。即使我们取出一条记录中的所有属性，我们仍然不能识别实体。想想看，这只是时间和数量。实际的项目实体集是一个弱实体集。我们借助类别项实体集中的重复主键来识别集合中的每个实体。|52785|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Weak entity exists to solve the multi-valued attributes problem. 

There are two types of multi-valued attributes. One is the simply many values for an objects such as a "hobby" as an attribute for a student. The student can have many different hobbies. If we leave the hobbies in the student entity set, "hobby" would not be unique any more. We create a separate entity set as hobby. Then we link the hobby and the student as we need. The hobby entity set is now an associative entity set. As to whether it is weak or not, we need to check whether each entity has enough unique identifiers to identify it. In many opinion, a hobby name can be enough to identify it.

The other type of multi-valued attribute problem does need a weak entity to fix it. Let's say an item entity set in a grocery inventory system. Is the item a category item or the actually item? It is an important question, because a customer can buy the same item at one time and at a certain amount, but he can also buy the same item at a different time with a different amount. Can you see it the same item but of different objects. The item now is a multi-valued attribute. We solve it by first separate the category item with the actual item. The two are now different entity sets. Category item has descriptive attributes of the item, just like the item you usually think of. Actual item can not have descriptive attributes any more because we can not have redundant problem. Actual item can only have date time and amount of the item. You can link them as you need. Now, let's talk about whether one is a weak entity of the other. The descriptive attributes are more than enough to identify each entity in the category item entity set. The actual item only has date time and amount. Even if we pull out all the attributes in a record, we still cannot identify the entity. Think about it is just time and amount. The actual item entity set is a weak entity set. We identify each entity in the set with the help of duplicate prime key from the category item entity set.

blocks|key|2535473|text|./Database/DataModels/RelationalDataModel/WeakEntity|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2535474|它可能可以用两个因素编写：|2535475|2535476|DEPENDENCE:依赖于标识实体集的存在(总计，一对多relationship).|unordered-list-item|2535477|IDENTIFICATION:没有主键。它有一个部分键(或鉴别器)。它需要使用identification.|2535478|的另一个表的主键|2535479|如果我们考虑一个包含问题和答案的数据库，那么问题将是强实体，答案将是弱实体。因此，number+(id，text)和Answer+(number，question_id，text)将是我们的表。但是为什么答案的表格是一个弱实体呢？|2535480|问题表的|2535481|依赖项。每个答案都与一个问题(假设)相关，因此它不能单独存在。这就是为什么我们有这样的人，他们问一个问题并自己回答，这样他们就可以帮助其他人，并从问题的主键获得一些额外的likings.|2535482|Identification。人们将无法识别答案(假设其id是数字标识符)，因为一个问题可能由其标识符也存在于其他问题中的答案来回答。答题表主键：(number，question_id).|2535483|2535484|entityMap^0|0|1G|0|0|0|0|B|0|0|F|0|0|15|G|1M|W|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|14|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|L|3|M|5|K|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|N|3|O|5|6|7|1B|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|R|3|S|5|6|7|1H|8|@]|D|@]|E|$]]|$1|T|3|U|5|K|7|1I|8|@]|D|@]|E|$]]|$1|V|3|W|5|K|7|1J|8|@]|D|@]|E|$]]|$1|X|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Z|$]]

./Database/DataModels/RelationalDataModel/WeakEntity

It probably can be written in two factors:

<ul>
<li>DEPENDENCE: Depends on the existence of an identifying entity set (total, one-to-many relationship).</li>
<li>IDENTIFICATION: Does not have a primary key. It has a partial key (or discriminator). It needs to use the primary key of another table for identification.</li>
</ul>

If we would think of a database holding questions and answers, then the questions would be the strong entity and the answers would be the weak entity.
So, Question (id, text) and Answer (number, question_id, text) would be our tables. But why is the Answer's table a weak entity?

<ul>
<li>Dependence to the question table. Every answer is connected to one question (assumption) and so it cannot be on its own. That is why we have people who ask one question and answer it themselves so that they can help other people and get some extra likings.</li>
<li>Identification from the primary key of the question. One would not be able to identify an answer (assuming that its id is a number identifier) because a question might be answered by answers whose identifier might exist in other questions too. Primary key of the answer table: (number, question_id).</li>
</ul>

blocks|key|51670|text|弱实体也称为依赖实体，因为它的存在依赖于其他实体。这样的实体在E-R图中由一个双轮廓矩形表示。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|51671|强实体也称为独立实体。|51672|entityMap^0|0|3|0|0|3|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

Weak entities are also called dependent entities, since it's existence depends on other entities. Such entities are represented by a double outline rectangle in the E-R diagram.

Strong entities are also called independent entities.

blocks|key|51896|text|在浏览了几个小时的搜索引擎后，我发现了一个网站，上面有一个很棒的ERD示例：http://www.exploredatabase.com/2016/07/description-about-weak-entity-sets-in-DBMS.html|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|51897|我重建了急诊室。不幸的是，他们没有指定弱实体的主键。|51898|​|51899|📷|atomic|51900|51901|如果建筑物只能有一个且只能有一个公寓，则似乎不会创建(即丢弃)部分鉴别器房间号。|51902|entityMap|0|LINK|mutability|MUTABLE|url|http://www.exploredatabase.com/2016/07/description-about-weak-entity-sets-in-DBMS.html|1|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/0a8d2927330151d4ceadfbd573f82b15.png|imageAlt^0|12|2E|0|0|0|0|0|1|1|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|16|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|K|3|G|5|6|7|1B|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|1C|8|@]|9|@]|C|$]]|$1|N|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]]|O|$P|$5|Q|R|S|C|$T|U]]|V|$5|W|R|X|C|$Y|Z|10|-4]]]]

After browsing search engines for a few hours I came across a site with a great ERD example here: <a href="http://www.exploredatabase.com/2016/07/description-about-weak-entity-sets-in-DBMS.html" rel="nofollow noreferrer">http://www.exploredatabase.com/2016/07/description-about-weak-entity-sets-in-DBMS.html</a>

I've recreated the ERD. Unfortunately they did not specify the primary key of the weak entity.

<a href="https://i.stack.imgur.com/OtxEe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OtxEe.png" alt="enter image description here"></a>

If the building could only have one and only one apartment, then it seems the partial discriminator room number would not be created (i.e. discarded).

blocks|key|52038|text|弱实体类型:如果实体的实例不链接其他实体的实例就无法退出，则称为弱实体类型。它不能独立存在。例如:我们的PC依赖于我们，它不会用自己的电脑打开或关闭。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|52039|强实体类型:链接到任何其他实体类型的实例的实体称为强实体类型。它可以独立退出。例如:一个人可以做每件事，可以去任何地方，使用每件事|52040|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Weak Entity Type:
An entity whose instances cannot exits without being linked with instances of some other entity is called weak entity type. It cannot exist independently.
For example: Our PC is depend on us it will not open or close with its own.

Strong Entity Type:
An entity whose linked to the instances of any other entity type is called strong entity type. It can exit independently.
For example: A person can do every thing can go everywhere and use ever thing

blocks|key|2744971|text|可以不依赖于另一个数据对象的存在而存在的数据对象被称为强数据对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2744972|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

A data object that can exist without depending upon the existence of another data object is known as Strong Data Object.

blocks|key|51325|text|首先在ARC中引入了强/弱引用类型。在非ARC分配/保留中使用。强引用意味着您希望“拥有”使用此属性/变量引用的对象。只要您使用强引用指向此属性，编译器就会注意到分配给此属性的任何对象都不会被销毁。仅当您将属性设置为nil时，对象才会被销毁。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|51326|弱引用意味着你不想控制对象的生命周期，或者不想“拥有”对象。您引用的弱对象仅存在，因为至少有一个其他对象持有对它的强引用。一旦不再是这种情况，对象就会被销毁，你的弱属性会自动设置为零。iOS中最常见的弱引用用例是IBOutlets、委托等。|51327|有关更多信息，请参阅：http://www.informit.com/articles/article.aspx?p=1856389&seqNum=5|offset|length|51328|entityMap|0|LINK|mutability|MUTABLE|url|http://www.informit.com/articles/article.aspx?p=1856389&seqNum=5^0|0|0|B|1S|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

First Strong/Weak Reference types are introduced in ARC. In Non ARC assign/retain are being used.
A strong reference means that you want to "own" the object you are referencing with this property/variable. The compiler will take care that any object that you assign to this property will not be destroyed as long as you points to it with a strong reference. Only once you set the property to nil, the object get destroyed.

A weak reference means you signify that you don't want to have control over the object's lifetime or don't want to "own" object. The object you are referencing weakly only lives on because at least one other object holds a strong reference to it. Once that is no longer the case, the object gets destroyed and your weak property will automatically get set to nil. 
The most frequent use cases of weak references in iOS are for IBOutlets, Delegates etc.

For more info Refer : <a href="http://www.informit.com/articles/article.aspx?p=1856389&amp;seqNum=5" rel="nofollow">http://www.informit.com/articles/article.aspx?p=1856389&amp;seqNum=5</a>

I've tried to look on Google about a decent explanation of weak and strong entity type, but I haven't fully understood them.

Could someone give me an example of a strong and weak entity type?

Example of a strong and weak entity types

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我试着在谷歌上寻找关于弱和强实体类型的合理解释，但我还没有完全理解它们。谁能给我一个强实体类型和弱实体类型的例子？

问强实体类型和弱实体类型的示例
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回答 12

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