This is a special simple sentence. Special, can not be analyzed according to the subject-predicate sentence. This is called existential sentence. If you want to divide the components, the zoo is the subject, running out is the predicate, and a tiger is the object.
The reason why the word "le" is added can also be analyzed according to the above division method.
Running is an intransitive verb, so it cannot take an object directly. So, running a tiger, in short, is not going well.
By the way, tigers are no longer the object of running.
A tiger ran out of the zoo. The composition of this sentence is:
Zoo is the subject, escape is the predicate, and a tiger is the object. Can be seen as a supplement.
In fact, this is a problem caused by the particularity of modern Chinese. The structural division of subject, predicate and object can not be applied to all Chinese phenomena. I just can't do grammar analysis. This is the particularity of Chinese.
China people's thinking and language are often illogical. Unable to perform logical analysis.
It's good to understand the meaning. Leave me alone. These belong to those experts and scholars. They can only have different views.