From d270f23e51d8f19034e6f1c1591e06712b1a7d23 Mon Sep 17 00:00:00 2001
From: Jinjing Zhou <VoVAllen@users.noreply.github.com>
Date: Mon, 3 Jun 2024 22:15:10 -0700
Subject: [PATCH] Update readme (#7)

Signed-off-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>
---
 LICENSE   | 201 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 README.md |  75 +++++++++++++-------
 2 files changed, 251 insertions(+), 25 deletions(-)
 create mode 100644 LICENSE

diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d4911bd
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,201 @@
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright [2024] TensorChord
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
\ No newline at end of file
diff --git a/README.md b/README.md
index 30f560e..b7a4021 100644
--- a/README.md
+++ b/README.md
@@ -1,40 +1,37 @@
-# pg_bestmatch
+# pg_bestmatch.rs
 
-This PostgreSQL extension provides functionalities for BM25 text queries, allowing efficient full-text search by converting text into sparse vectors. This enables integration with vector search extensions such as `pgvecto.rs` or `pgvector`.
+This PostgreSQL extension provides functionalities for BM25 text queries, generateing BM25 statistic sparse vectors for text. BM25 outperforms dense vector-based retrieval methods in many [RAG benchmark tasks](https://hazyresearch.stanford.edu/blog/2024-05-20-m2-bert-retrieval).
 
-## Installation
+User can use vector search extensions such as `pgvecto.rs` or `pgvector` for efficient searches in postgres.
 
-```sql
-CREATE EXTENSION pg_bestmatch;
-SET search_path TO public, bm_catalog;
-```
+> [!IMPORTANT]  
+> Based on our initial tests, HNSW indexing does not support the sparse vectors generated by BM25 very well. The high sparsity prevents effective navigation within the graph.
 
-## Build from source
 
-Before building, you should have `PostgreSQL`, `Rust` and `Cargo` installed on your system.
-
-1. Install `cargo-pgrx`.
-
-```sh
-cargo install cargo-pgrx --version v0.12.0-alpha.1
-```
+* [Installation](#installation)
+* [How does it work?](#how-does-it-work)
+* [Usage](#usage)
+* [Build from source](#build-from-source)
+* [Comparison with pg_search](#comparison-with-pg_search)
+* [Reference](#Reference)
 
-2. Initialize `cargo-pgrx`.
+## Installation
 
-```sh
-cargo pgrx init --pg16=$(which pg_config)   # assuming that you have PostgreSQL 16 installed
+```sql
+CREATE EXTENSION pg_bestmatch;
+SET search_path TO public, bm_catalog;
 ```
 
-3. Build.
-
-```sh
-cargo pgrx install --release    # if you want to install it on your machine
-cargo pgrx package  # if you want to package `pg_bestmatch`
-```
+## How does it work?
+- Create an BM25 statistics based on your document set by `bm25_create(table_name, column_name, statistic_name);`. It will create a materilized view to record the stats. 
+- Generate document sparse vector by `bm25_document_to_svector(statistic_name, passage)`
+- For query, generate query sparse vector `bm25_query_to_svector(statistic_name, query)`
+- Calculate the score by dot product between the query sparse vector and the document sparse vector
+- Currently we use huggingface tokenizer with `bert-base-uncased` vocabulary set to tokenize words. Might support more configuration on tokenizer in the future.
 
 ## Usage
 
-Here is an example workflow demonstrating the usage of this extension with the example of [Stanford LoCo benchmark](https://hazyresearch.stanford.edu/blog/2024-01-11-m2-bert-retrieval).
+Here is an example workflow demonstrating the usage of this extension with the example of [Stanford LoCo benchmark](https://hazyresearch.stanford.edu/blog/2024-05-20-m2-bert-retrieval).
 
 0. Load the dataset. Here is a script for you if you want to experience `pg_bestmatch` with the dataset.
 
@@ -123,6 +120,34 @@ SELECT sum((array[answer_pids] = array(SELECT pid FROM documents WHERE queries.d
 
 This workflow showcases how to leverage BM25 text queries and vector search in PostgreSQL using this extension. The Top 1 recall of BM25 on this dataset is `0.77`. If you reproduce the result, your operations are correct.
 
+
+## Build from source
+
+Before building, you should have `PostgreSQL`, `Rust` and `Cargo` installed on your system.
+
+1. Install `cargo-pgrx`.
+
+```sh
+cargo install cargo-pgrx --version v0.12.0-alpha.1
+```
+
+2. Initialize `cargo-pgrx`.
+
+```sh
+cargo pgrx init --pg16=$(which pg_config)   # assuming that you have PostgreSQL 16 installed
+```
+
+3. Build.
+
+```sh
+cargo pgrx install --release    # if you want to install it on your machine
+cargo pgrx package  # if you want to package `pg_bestmatch`
+```
+
+## Comparison with pg_search 
+- `pg_bestmatch.rs` only provides methods for generating sparse vectors and does not support index-based search (which can be achieved by pgvecto.rs or pgvector). 
+- `pg_search` performs BM25 retrieval via the external `tantivy` engine, which may have limitations when combined with transactions, filters, or JOIN operations. Since `pg_bestmatch.rs` is entirely native to Postgres, it offers full compatibility with these operations inside postgres.
+
 ## Reference
 
 - `tokenize`