I'm studying SSVM (Structured SVMs). On my book is stated that Structured SVM is an extension of the SVM, in which

Each sample is assigned to a structured output label z ∈ K, e.g. partitions, trees, lists, etc.

It's not clear to me what a structured output label is.

Could you provide me with an explanation of this term along with some tangible examples?

  • $\begingroup$ I have seen an example of a parser but it's not clear to me $\endgroup$ – Tommaso Bendinelli Dec 27 '18 at 7:59

Structured Learning is basically learning prediction functions that is used to map input data to complex output space. The regular SVMs are used for univariate classification where input is mapped to atomic labels or regression where input is mapped to vectors or scalar numbers. Structured Output learning extends this very process to more complex output spaces like: - Multi Class Classification : where output is a "set" of class labels.
- Object localization Problem : where output space defines bounding boxes. - Sequence alignment problems in protein homology detection, - Parts of Speech tagging in NLP , etc.

Hope this clears it up for you.

  • $\begingroup$ Thank you for answering. I have two questions: So a multi class classification problem is considered a structured output label? And What do you mean by bounding boxes with regards to object localization problem? $\endgroup$ – Tommaso Bendinelli Dec 27 '18 at 9:47
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    $\begingroup$ Yes, in multiclass problem, you're outputting a list of say n classes, with each index showing the probability of the object being in that class. So its a vector. Hence its a structured output. With object localization problem, suppose you have to identify where a car is located in a certain image. The output you'll be providing is a set of bounding boxes for the car. For this ,you'll say , provide the coordinates of top left corner and bottom right corner of the bounding box. So output is a tuple. Hence a structured output. $\endgroup$ – Mohit Banerjee Dec 27 '18 at 9:56
  • $\begingroup$ Okay thanks, Mohit, so basically any output that it's not scalar can be considered structured. $\endgroup$ – Tommaso Bendinelli Dec 27 '18 at 10:15

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