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Intelligent Information Retrieval
CSC 575

Assignment 3
Due: Sunday, February 19, 2023

  1. [50 pts] Query Expansion and Relevance Feedback

    In this problem you will explore different approaches to query expansion and modification. First, you will implement the Rocchio's method for relevance feedback in vector space retrieval models (parts a-c below). Then, you will explore the idea of Automatic Global Analysis for query expansion based on associated terms (parts d-e below).

    We assume that we have a set of documents that have already been preprocessed (basic tokenization and stemming) with each document given as a single line in a text file. For testing purposes, we will use this set of test documents.
    1. First, read in the documents and create a document by term matrix (with 15 documents as rows and 16 unique terms as columns with entries corresponding to raw term counts in each document. Be sure to organize your matrix so that terms (or term indices) are listed in alphabetical order. The first 5 documents in the matrix (documents 0 through 4) should look like this table. Provide the full document-term matrix in your submission. Note that your program should be general and work with any set of N documents and M terms, generating a NxM matrix.

    2. Next consider a query Q = "relev feedback queri relev" issued by a hypothetical user, and suppose that after getting back the search results the user provides relevance feedback on the following documents

      Relevant docs (R): [0, 2, 8, 13]
      Non-relevant docs (NR): [6, 7, 14]

      Write a function modify_query(Q, R, NR, alpha, beta) that returns a new query vector (over terms) using Rocchio's relevance feedback method. The parameters for this function are described below:

      Q: the original M-dimensional query vector. For example, the above query Q will result in the following vector:

      Q = [0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 2, 0, 0, 0, 0]

      or, in more readable form as this vector with term dimensions displayed.

      : The set of documents identified as relevant by the user (this may be represented a submatrix of the original doc-term matrix with only the relevant documents included).

      NR: The set of documents identified as non-relevant by the user.

      alpha and beta: positive and negative feedback coefficients (weights), respectively.

      You may find it useful to write a helper function to compute the centroid vector associated with a subset of documents (to compute centroids for R and NR).

      Again, your function should work with any query and any specified sets of relevant and non-relevant documents. But, to demonstrate your functions, use it to generate a new query Q1, given the above query Q, documents sets R and NR; and with alpha = 0.5 and beta = 0.25. Provide your results displaying both Q and Q1 using the term dimensions in the original doc-term matrix.

    3. Next, using Cosine similarity, compute the ranked list of returned documents for each of the queries Q and Q1, using the full set of the document in the original doc-term matrix. Explain the most significant promotion and the most significant demotion in the relative rankings of the documents.

    4. Write a program/function to create a term-by-term association matrix  from a given document-term matrix that could be used for query expansion based on Automatic Global Analysis (see slide 7-12 of the lecture notes: CSC575-501 - Query Operations). Note that an intermediate non-normalized term-term association matrix can be created by multiplying the transpose of the document-term matrix (which is a term-document matrix) by the document-term matrix, itself. This will result in a symmetric term-term matrix where each entry corresponds to the dot product of the corresponding terms. The final association matrix must be computed by normalizing the entries using the Jaccard coefficient (slide 9). Test your program on the document-term matrix from part a, above. You should provide the full normalized term-by-term association matrix, S,  as part if your submission. For partial credit, you can also provide your intermediate non-normalized term-by-term matrix (of dot products).

    5. Next, given the normalized term-term association matrix and a query containing a subset of the terms in the matrix, write a program that outputs an expanded query using global analysis with given value of n (i.e., for each term T in the initial query, the top n most similar terms to T should be added to the expanded query, if not already present). Test your program using the query: Q0 = ['relev', 'retriev'] with values of n = 1 and n = 2.  Your output, submit with your assignment should clearly indicate related terms to be added to the query Q0 corresponding to each term in the original query. A sample output for a different test query is given in this example.

  2. [50 pts] Content-Based Recommendation

    In this problem, you will implement your own version of a rudimentary content-based recommender system that will use the K-Nearest-Neighbor (KNN) strategy to recommend items of interest to a user. A content-based recommender can be viewed as a type of IR system that, instead of an explicit user-specified query, uses a learned user profile to recommend similar items. As in other IR systems, the items to be recommended as well as the user's profile are represented as vectors over a set of features. Features may be textual tokens (when items are documents), but they can also be other types of "content" features that represent the characteristics of the items. For this assignment we will use a preprocessed data set from Spotify where various songs are represented in terms of different musical and acoustic features. We will assume that, for each user, the system maintains a list of songs liked or played by the user in the past (e.g., a playlist). A user's profile will be represented as the aggregate vector representation of the songs in the user's playlist. The main task for the system is to match the user's profile with representations of the available songs and recommend the top k songs most similar to that profile. The necessary data files are available in the archive: Spotify_Preprocessed.zip. Be sure to review the "readme" file which provides a more detailed description of each file.

    The basic tasks for this problem are the following:

    1. Write a function knn(item, Data, K) that given the vector representation of an item (in this case a song), the Data matrix representing song features (from the file: "Spotify_Numeric.csv"), and the number of neighbors "K", will return the indices of the K most similar songs to "item" in decreasing order of similarity, along with the corresponding similarity values. Your implementation should use cosine similarity function to find the K nearest-neighbors. You can implement your own cosine function or use an external library. Use the information contained in the file "Spotify_Metadata.csv" to include information about the recommended songs in your output (such song name, artist, song mood(s), etc.). For example, given an item represented as the following feature vector:

      item = [0.1, 0.5, 0.2, 0.5, 0.0, 0.5, 0.0, 0.8, 1.0, 0.2, 0.5, 0.5, 0.3]

      the knn function might produce an output similar to this example. Demonstrate your knn function by producing the top 10 most similar songs the an item with the following feature vector:

      item = [0.8, 0.1, 0.7, 0.0, 0.5, 0.1, 0.5, 0.2, 0.0, 1.0, 0.1, 0.2, 0.7]

    2. Next, write a program/function to generate a list of top K recommendations for a given user, given the user's previously recorded playlist. The core of your "recommend" function is a call to the knn function described above. However, the recommend function should take as input not a single item, but a user's playlist containing the indices of songs previously played by the user (similar to user playlists in the file: "Spotify_Users.txt"). The "recommend" function should generate an aggregate representation of the lit of items by computing the centroid (mean) vector corresponding to vector representations of the songs in the user's playlist. This aggregate representation is then used as input to the knn function to generate the k most similar songs to the playlist as recommendations for the user. For example, given a user play list:

      playlist = [1133, 1136, 1150, 1157, 1164, 1261, 1279, 1360]

      and K = 10, the recommend function might generate an output similar to this example. To demonstrate your program, run your "recommend" function to generate top 10 recommendations for the user 0 (first row in the "Spotify_Users.txt") and for user 7 (8th row in the same file).

    3. Write a program/function to evaluate the accuracy of your recommender system using Precision and Recall metrics. We will use the user playlists in "Spotify_Users.txt" as our test data. For each user, you should divide the playlist in half with the first half to be used as the user profile for input into the "recommend" function, and the 2nd half as the set of relevant items for that user that are held out for testing purposes (note that the list of songs in each playlist has already been randomized). Ideally, we would like the recommend function to generate as many of the held-out items as possible for each user, but of course, the number of recommendations, K, will be a factor. In this context, precision and recall may be computed as follows.

      Lets' denote the set of relevant recommendations for a single user u as Rel_u defined as the set of held out items (2nd half of user's playlist). Let Rec_u denote the list of top-k recommended items for user u generated by the recommender with the first half of user's profile as input. Precision@k for user u is defined as |intersect(Rec_u,  Rel_u|)/|Rec_u| which is the same as the number of common items between recommendation list and the hold-out test set, divided by k. Recall@k for user u is defined as |intersect(Rec_u,  Rel_u|)/|Rel_u|, i.e, the number of common items between the k recommended items and the test set, divided by the size of the test set. To perform evaluation of the system, average precision@k and recall@k values (for a specific value of k) must be computed across all test users (in this case the 20 playlists given in "Spotify_Users.txt"). This will produce avg_precision@k and avg_recall@k. Finally, to tune the system, avg_precision@k and avg_recall@k must be computed for a range of values of k. You should write your own evaluation function (rather than using existing libraries) and you should produce a chart with avg precision and avg recall values relative to values of k. You should use [1, 100] as your range of values of k. This example shows what your results might look like (though this is not the expected result for the provided data set).

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Copyright ©, Bamshad Mobasher, DePaul University.