allenai / nlpstack   1.19


NLP toolkit (tokenizer, POS-tagger, parser, etc.)

Scala versions: 2.11 2.10

NLP Stack

This contains our basic stack of NLP tools. You can play with them here.

We have general interfaces on each tool so we have a clear definition of the inputs and outputs of each tool and so we can change the underlying implementation of a tool.

Each tool also has a serialization format for its output. For example, there is a dependency string format and a chunked sentence string format.

Getting started

  1. Add NLPStack to your dependencies. NLPStack comes as a collection of multiple tools (see below). To declare dependencies, you can use this code in your Build.scala file:

    libraryDependencies += "org.allenai.nlpstack" %% "nlpstack-core" % "0.x"
    libraryDependencies += "org.allenai.nlpstack" %% "nlpstack-parse" % "0.x"
    libraryDependencies += "org.allenai.nlpstack" %% "nlpstack-postag" % "0.x"

    As an option, you can define a function for the various nlpstack components, and use them like this:

    def nlpstackModule(id: String) = "org.allenai.nlpstack" %% s"nlpstack-${id}" % "0.x"
    libraryDependencies += nlpstackModule("parse")
  2. Start using NLPStack. Here is a quick code snippet that parses a sentence:

    import org.allenai.nlpstack.tokenize.defaultTokenizer
    import org.allenai.nlpstack.postag.defaultPostagger
    import org.allenai.nlpstack.parse.defaultDependencyParser
    /* ... */
    val tokens = defaultTokenizer.tokenize(
      "I was wondering why the ball kept getting bigger and bigger, and then it hit me.")
    val postaggedTokens = defaultPostagger.postagTokenized(tokens)
    val dependencyGraph = defaultDependencyParser.dependencyGraphPostagged(postaggedTokens)

Folder Layout

  1. tools: this project contains the main Nlpstack code.
  2. webapp: a web application for running tools and visualizing serialized representations.

Tools in the Kit

Presently the AI Toolkit includes the following tools.

  1. Tokenizer. Break a sentence into "word" tokens.
  2. Lemmatizer. Associate a base form to a token or a Part-of-Speech (POS) tagged token. The results will be more accurate if POS tags are available.
  3. Postagger. Associate a POS tag with a token.
  4. Chunker. Associate chunk ranges with POS-tagged tokens.
  5. Dependency Parser. Construct dependencies between POS-tagged tokens.
  6. Segmenter. Split a body of text into sentences.

Each tool includes:

  • An API so it can be called programatically.
  • A CLI application so it can be run in batch.
  • A simple REST server so it can be called remotely.

Tool Subprojects

Nlpstack is split up into multiple subprojects to minimize the number of dependencies needed to install components. The source for each of these is in tools/${projectName}.

tools-core: This contains all of the APIs needed for interoperating with Nlpstack, but none of the implementations. tools-segment: Implementation of the segmenter. Depends on core. tools-lemmatize: Implementation of the lemmatizer. Depends on core. tools-tokenize: Implementation of the tokenizer. Depends on core. tools-postag: Implementation of the POS tagger. Depends on tokenize. tools-chunk: Implementation of the sentence chunker. Depends on postag. tools-parse: Implementation of the dependency parser. Depends on postag.

These each produce a single artifact, named nlptools-${projectName}. A client should depend on every implementation they will be using, as well as nlpstack-core.

These all use the group org.allenai.nlpstack.

So, if you wanted to use the tokenizer, you should have the dependencies (in sbt):

"org.allenai.nlpstack" %% "nlpstack-core" % "2014.6.23-1-SNAPSHOT"
"org.allenai.nlpstack" %% "nlpstack-tokenize" % "2014.6.23-1-SNAPSHOT"

The current version is in version.sbt.

Parsing API Details

The example in "Getting Started" shows how to generate a dependency graph from a sentence. The graph object itself contains dependency nodes with integer IDs. These IDs can be used to index the original tokens given to the parser.

If you want to have lemmatized token information, you'll want to run the tokens through a lemmatizer:

import org.allenai.nlpstack.lemmatize.MorphaStemmer

val lemmatizer = new MorphaStemmer()
val lemmatizedTokens = postaggedTokens map { lemmatizer.lemmatizePostaggedToken }

Once you have lemmatized tokens, you can build a new dependency graph with token information contained in the nodes:

val dependencyGraphWithTokenInfo = dependencyGraph.tokenized(lemmatizedTokens)

Releasing new versions

This project releases to Maven Central rather than to our own repository. To do this, you need a bit of setup.

  1. You need the signing keys to publish software with. You can find them in the ai2-secure bucket in S3 under the key Sonatype Key Copy that file to ~/.sbt/gpg/ and extract it there.
  2. You need the passphrase for that key pair. It's defined as an array, which is a little weird, and goes into another location in ~/.sbt. The line defining it is in passwords.txt in the ai2-secure bucket. Copy that line into ~/.sbt/0.13/allenai.sbt (or into some other .sbt if you like).
  3. To use the passphrase, we have to enable the sbt-pgp plugin. Put the following line into ~/.sbt/0.13/plugins/gpg.sbt: addSbtPlugin("com.jsuereth" % "sbt-pgp" % "1.0.0")
  4. We also need credentials to the sonatype repository. We get those with the following line in ~/.sbt/0.13/sonatypt.sbt: credentials += Credentials("Sonatype Nexus Repository Manager", "", "allenai-role", "<password>"). You find this password in the same password.txt file from above.

Now, you need to register your GPG key.

  1. Start SBT in the nlpstack project

  2. At the SBT prompt, type:

    > pgp-cmd send-key [TAB]
    Paul Allen Institute for Artificial Intelligence <account>

    When you hit [TAB], SBT should print out the available key and its ID on the second line (in the example above, abcdefg. Enter the id:

    > pgp-cmd send-key abcdefg hkp:// [ENTER]

With this, you should be ready to run sbt release on the common project. When you do, it will upload the build artifacts to a staging repository on When it's done, you have to go there and first close, and then release, the staging repository. That initiates the upload to Maven Central, which will take about 10 minutes.

  1. Go to
  2. Log in with username allenai-role, and the password from the password.txt file. This is the same password you used in step 4 above.
  3. Click "staging repositories" on the left.
  4. Use the search bar at the top right to search for "allenai".
  5. Find your staging repository and confirm that it has the contents you expect. Then, select it and click "Close". Closing takes a few minutes. Then you can see how the closing process went under "Activity". It sends an email to [email protected] when it's done.
  6. When it is done, select the repository again and hit "Release".
  7. You should see the new version appear under

You are done!