Assigned: Mon, Sept 17
Due: Wed, Sept 26 11:59 PM EDT
In the lab assignments in 6.830 you will write a basic database management system called SimpleDB. For this lab, you will focus on implementing the core modules required to access stored data on disk; in future labs, you will add support for various query processing operators, as well as transactions, locking, and concurrent queries.
SimpleDB is written in Java. We have provided you with a set of mostly unimplemented classes and interfaces. You will need to write the code for these classes. We will grade your code by running a set of system tests written using JUnit. We have also provided a number of unit tests, which we will not use for grading but that you may find useful in verifying that your code works.
The remainder of this document describes the basic architecture of SimpleDB, gives some suggestions about how to start coding, and discusses how to hand in your lab.
We strongly recommend that you start as early as possible on this lab. It requires you to write a fair amount of code!
Start by downloading the code for lab 1 from the course GitHub repository by following the instructions here.
These instructions are written for Athena or any other Unix-based platform (e.g., Linux, MacOS, etc.) Because the code is written in Java, it should work under Windows as well, although the directions in this document may not apply.
We have included Section 1.2 on using the project with Eclipse.
SimpleDB uses the Ant build tool to compile the code and run tests. Ant is similar to make, but the build file is written in XML and is somewhat better suited to Java code. Most modern Linux distributions include Ant. Under Athena, it is included in the sipb locker, which you can get to by typing add sipb at the Athena prompt. Note that on some versions of Athena you must also run add -f java to set the environment correctly for Java programs. See the Athena documentation on using Java for more details.
To help you during development, we have provided a set of unit tests in addition to the end-to-end tests that we use for grading. These are by no means comprehensive, and you should not rely on them exclusively to verify the correctness of your project (put those 6.170 skills to use!).
To run the unit tests use the test build target:
$ cd [project-directory]
$ # run all unit tests
$ ant test
$ # run a specific unit test
$ ant runtest -Dtest=TupleTest
You should see output similar to:
build output...
test:
[junit] Running simpledb.CatalogTest
[junit] Testsuite: simpledb.CatalogTest
[junit] Tests run: 2, Failures: 0, Errors: 2, Time elapsed: 0.037 sec
[junit] Tests run: 2, Failures: 0, Errors: 2, Time elapsed: 0.037 sec
... stack traces and error reports ...
The output above indicates that two errors occurred during compilation; this is because the code we have given you doesn't yet work. As you complete parts of the lab, you will work towards passing additional unit tests.
If you wish to write new unit tests as you code, they should be added to the test/simpledb directory.
For more details about how to use Ant, see the [manual](http://ant.apache.org/manual/). The [Running Ant](http://ant.apache.org/manual/running.html) section provides details about using the `ant` command. However, the quick reference table below should be sufficient for working on the labs.
| Command | Description |
|---|---|
| ant | Build the default target (for simpledb, this is dist). |
| ant -projecthelp | List all the targets in build.xml with descriptions. |
| ant dist | Compile the code in src and package it in dist/simpledb.jar. |
| ant test | Compile and run all the unit tests. |
| ant runtest -Dtest=testname | Run the unit test named testname. |
| ant systemtest | Compile and run all the system tests. |
| ant runsystest -Dtest=testname | Compile and run the system test named testname. |
If you are under windows system and don't want to run ant tests from command line, you can also run them from eclipse. Right click build.xml, in the targets tab, you can see "runtest" "runsystest" etc. For example, select runtest would be equivalent to "ant runtest" from command line. Arguments such as "-Dtest=testname" can be specified in the "Main" Tab, "Arguments" textbox. Note that you can also create a shortcut to runtest by copying from build.xml, modifying targets and arguments and renaming it to, say, runtest_build.xml.
We have also provided a set of end-to-end tests that will eventually be used for grading. These tests are structured as JUnit tests that live in the test/simpledb/systemtest directory. To run all the system tests, use the systemtest build target:
$ ant systemtest
... build output ...
[junit] Testcase: testSmall took 0.017 sec
[junit] Caused an ERROR
[junit] expected to find the following tuples:
[junit] 19128
[junit]
[junit] java.lang.AssertionError: expected to find the following tuples:
[junit] 19128
[junit]
[junit] at simpledb.systemtest.SystemTestUtil.matchTuples(SystemTestUtil.java:122)
[junit] at simpledb.systemtest.SystemTestUtil.matchTuples(SystemTestUtil.java:83)
[junit] at simpledb.systemtest.SystemTestUtil.matchTuples(SystemTestUtil.java:75)
[junit] at simpledb.systemtest.ScanTest.validateScan(ScanTest.java:30)
[junit] at simpledb.systemtest.ScanTest.testSmall(ScanTest.java:40)
... more error messages ...
This indicates that this test failed, showing the stack trace where the error was detected. To debug, start by reading the source code where the error occurred. When the tests pass, you will see something like the following:
$ ant systemtest
... build output ...
[junit] Testsuite: simpledb.systemtest.ScanTest
[junit] Tests run: 3, Failures: 0, Errors: 0, Time elapsed: 7.278 sec
[junit] Tests run: 3, Failures: 0, Errors: 0, Time elapsed: 7.278 sec
[junit]
[junit] Testcase: testSmall took 0.937 sec
[junit] Testcase: testLarge took 5.276 sec
[junit] Testcase: testRandom took 1.049 sec
BUILD SUCCESSFUL
Total time: 52 seconds
It is likely you'll want to create your own tests and your own data tables to test your own implementation of SimpleDB. You can create any .txt file and convert it to a .dat file in SimpleDB's HeapFile format using the command:
$ java -jar dist/simpledb.jar convert file.txt N
where file.txt is the name of the file and N is the number of columns in the file. Notice that file.txt has to be in the following format:
int1,int2,...,intN
int1,int2,...,intN
int1,int2,...,intN
int1,int2,...,intN
...where each intN is a non-negative integer.
To view the contents of a table, use the print command:
$ java -jar dist/simpledb.jar print file.dat N
where file.dat is the name of a table created with the convert command, and N is the number of columns in the file.
Eclipse is a graphical software development environment that you might be more comfortable with working in. The instructions we provide were generated by using Eclipse for Java Developers (not the enterprise edition) with Java 1.7.
Setting the Lab Up in Eclipse
- Once Eclipse is installed, start it, and note that the first screen asks you to select a location for your workspace (we will refer to this directory as $W). Select the directory containing your simple-db-hw repository.
- In Eclipse, select File->New->Project->Java->Java Project, and push Next.
- Enter "simple-db-hw" as the project name.
- On the same screen that you entered the project name, select "Create project from existing source," and browse to $W/simple-db-hw.
- Click finish, and you should be able to see "simple-db-hw" as a new project in the Project Explorer tab on the left-hand side of your screen. Opening this project reveals the directory structure discussed above - implementation code can be found in "src," and unit tests and system tests found in "test."
Note: that this class assumes that you are using the official Oracle release of Java. This is the default on MacOS X, and for most Windows Eclipse installs; but many Linux distributions default to alternate Java runtimes (like OpenJDK). Please download the latest Java8 updates from Oracle Website, and use that Java version. If you don't switch, you may see spurious test failures in some of the performance tests in later labs.
Running Individual Unit and System Tests
To run a unit test or system test (both are JUnit tests, and can be initialized the same way), go to the Package Explorer tab on the left side of your screen. Under the "simple-db-hw" project, open the "test" directory. Unit tests are found in the "simpledb" package, and system tests are found in the "simpledb.systemtests" package. To run one of these tests, select the test (they are all called *Test.java - don't select TestUtil.java or SystemTestUtil.java), right click on it, select "Run As," and select "JUnit Test." This will bring up a JUnit tab, which will tell you the status of the individual tests within the JUnit test suite, and will show you exceptions and other errors that will help you debug problems.
Running Ant Build Targets
If you want to run commands such as "ant test" or "ant systemtest," right click on build.xml in the Package Explorer. Select "Run As," and then "Ant Build..." (note: select the option with the ellipsis (...), otherwise you won't be presented with a set of build targets to run). Then, in the "Targets" tab of the next screen, check off the targets you want to run (probably "dist" and one of "test" or "systemtest"). This should run the build targets and show you the results in Eclipse's console window.
Before beginning to write code, we strongly encourage you to read through this entire document to get a feel for the high-level design of SimpleDB.
You will need to fill in any piece of code that is not implemented. It will be obvious where we think you should write code. You may need to add private methods and/or helper classes. You may change APIs, but make sure our grading tests still run and make sure to mention, explain, and defend your decisions in your writeup.
In addition to the methods that you need to fill out for this lab, the class interfaces contain numerous methods that you need not implement until subsequent labs. These will either be indicated per class:
// Not necessary for lab1.
public class Insert implements DbIterator {or per method:
public boolean deleteTuple(Tuple t) throws DbException {
// some code goes here
// not necessary for lab1
return false;
}The code that you submit should compile without having to modify these methods.
We suggest exercises along this document to guide your implementation, but you may find that a different order makes more sense for you.
Here's a rough outline of one way you might proceed with your SimpleDB implementation:
- Implement the classes to manage tuples, namely Tuple, TupleDesc. We have already implemented Field, IntField, StringField, and Type for you. Since you only need to support integer and (fixed length) string fields and fixed length tuples, these are straightforward.
- Implement the Catalog (this should be very simple).
- Implement the BufferPool constructor and the getPage() method.
- Implement the access methods, HeapPage and HeapFile and associated ID classes. A good portion of these files has already been written for you.
- Implement the operator SeqScan.
- At this point, you should be able to pass the ScanTest system test, which is the goal for this lab.
Section 2 below walks you through these implementation steps and the unit tests corresponding to each one in more detail.
As you look through the interfaces we have provided you, you will see a number of references to locking, transactions, and recovery. You do not need to support these features in this lab, but you should keep these parameters in the interfaces of your code because you will be implementing transactions and locking in a future lab. The test code we have provided you with generates a fake transaction ID that is passed into the operators of the query it runs; you should pass this transaction ID into other operators and the buffer pool.
SimpleDB consists of:
- Classes that represent fields, tuples, and tuple schemas;
- Classes that apply predicates and conditions to tuples;
- One or more access methods (e.g., heap files) that store relations on disk and provide a way to iterate through tuples of those relations;
- A collection of operator classes (e.g., select, join, insert, delete, etc.) that process tuples;
- A buffer pool that caches active tuples and pages in memory and handles concurrency control and transactions (neither of which you need to worry about for this lab); and,
- A catalog that stores information about available tables and their schemas.
SimpleDB does not include many things that you may think of as being a part of a "database." In particular, SimpleDB does not have:
- (In this lab), a SQL front end or parser that allows you to type queries directly into SimpleDB. Instead, queries are built up by chaining a set of operators together into a hand-built query plan (see Section 2.7). We will provide a simple parser for use in later labs.
- Views.
- Data types except integers and fixed length strings.
- (In this lab) Query optimizer.
- (In this lab) Indices.
In the rest of this Section, we describe each of the main components of SimpleDB that you will need to implement in this lab. You should use the exercises in this discussion to guide your implementation. This document is by no means a complete specification for SimpleDB; you will need to make decisions about how to design and implement various parts of the system. Note that for Lab 1 you do not need to implement any operators (e.g., select, join, project) except sequential scan. You will add support for additional operators in future labs.
The Database class provides access to a collection of static objects that are the global state of the database. In particular, this includes methods to access the catalog (the list of all the tables in the database), the buffer pool (the collection of database file pages that are currently resident in memory), and the log file. You will not need to worry about the log file in this lab. We have implemented the Database class for you. You should take a look at this file as you will need to access these objects.
Tuples in SimpleDB are quite basic. They consist of a collection of `Field` objects, one per field in the `Tuple`. `Field` is an interface that different data types (e.g., integer, string) implement. `Tuple` objects are created by the underlying access methods (e.g., heap files, or B-trees), as described in the next section. Tuples also have a type (or schema), called a _tuple descriptor_, represented by a `TupleDesc` object. This object consists of a collection of `Type` objects, one per field in the tuple, each of which describes the type of the corresponding field.
Implement the skeleton methods in:
- src/simpledb/TupleDesc.java
- src/simpledb/Tuple.java
At this point, your code should pass the unit tests TupleTest and TupleDescTest. At this point, modifyRecordId() should fail because you havn't implemented it yet.
The catalog (class Catalog in SimpleDB) consists of a list of the tables and schemas of the tables that are currently in the database. You will need to support the ability to add a new table, as well as getting information about a particular table. Associated with each table is a TupleDesc object that allows operators to determine the types and number of fields in a table.
The global catalog is a single instance of Catalog that is allocated for the entire SimpleDB process. The global catalog can be retrieved via the method Database.getCatalog(), and the same goes for the global buffer pool (using Database.getBufferPool()).
Implement the skeleton methods in:
- src/simpledb/Catalog.java
At this point, your code should pass the unit tests in CatalogTest.
The buffer pool (class `BufferPool` in SimpleDB) is responsible for caching pages in memory that have been recently read from disk. All operators read and write pages from various files on disk through the buffer pool. It consists of a fixed number of pages, defined by the `numPages` parameter to the `BufferPool` constructor. In later labs, you will implement an eviction policy. For this lab, you only need to implement the constructor and the `BufferPool.getPage()` method used by the SeqScan operator. The BufferPool should store up to `numPages` pages. For this lab, if more than `numPages` requests are made for different pages, then instead of implementing an eviction policy, you may throw a DbException. In future labs you will be required to implement an eviction policy.
The Database class provides a static method, Database.getBufferPool(), that returns a reference to the single BufferPool instance for the entire SimpleDB process.
Implement the getPage() method in:
- src/simpledb/BufferPool.java
We have not provided unit tests for BufferPool. The functionality you implemented will be tested in the implementation of HeapFile below. You should use the DbFile.readPage method to access pages of a DbFile.
Access methods provide a way to read or write data from disk that is arranged in a specific way. Common access methods include heap files (unsorted files of tuples) and B-trees; for this assignment, you will only implement a heap file access method, and we have written some of the code for you.
A HeapFile object is arranged into a set of pages, each of which consists of a fixed number of bytes for storing tuples, (defined by the constant BufferPool.DEFAULT_PAGE_SIZE), including a header. In SimpleDB, there is one HeapFile object for each table in the database. Each page in a HeapFile is arranged as a set of slots, each of which can hold one tuple (tuples for a given table in SimpleDB are all of the same size). In addition to these slots, each page has a header that consists of a bitmap with one bit per tuple slot. If the bit corresponding to a particular tuple is 1, it indicates that the tuple is valid; if it is 0, the tuple is invalid (e.g., has been deleted or was never initialized.) Pages of HeapFile objects are of type HeapPage which implements the Page interface. Pages are stored in the buffer pool but are read and written by the HeapFile class.
SimpleDB stores heap files on disk in more or less the same format they are stored in memory. Each file consists of page data arranged consecutively on disk. Each page consists of one or more bytes representing the header, followed by the page size bytes of actual page content. Each tuple requires tuple size * 8 bits for its content and 1 bit for the header. Thus, the number of tuples that can fit in a single page is:
_tuples per page_ = floor((_page size_ * 8) / (_tuple size_ * 8 + 1))
Where tuple size is the size of a tuple in the page in bytes. The idea here is that each tuple requires one additional bit of storage in the header. We compute the number of bits in a page (by mulitplying page size by 8), and divide this quantity by the number of bits in a tuple (including this extra header bit) to get the number of tuples per page. The floor operation rounds down to the nearest integer number of tuples (we don't want to store partial tuples on a page!)
Once we know the number of tuples per page, the number of bytes required to store the header is simply:
headerBytes = ceiling(tupsPerPage/8)
The ceiling operation rounds up to the nearest integer number of bytes (we never store less than a full byte of header information.)
The low (least significant) bits of each byte represents the status of the slots that are earlier in the file. Hence, the lowest bit of the first byte represents whether or not the first slot in the page is in use. The second lowest bit of the first byte represents whether or not the second slot in the page is in use, and so on. Also, note that the high-order bits of the last byte may not correspond to a slot that is actually in the file, since the number of slots may not be a multiple of 8. Also note that all Java virtual machines are big-endian.
Implement the skeleton methods in:
- src/simpledb/HeapPageId.java
- src/simpledb/RecordID.java
- src/simpledb/HeapPage.java
Although you will not use them directly in Lab 1, we ask you to implement getNumEmptySlots() and isSlotUsed() in HeapPage. These require pushing around bits in the page header. You may find it helpful to look at the other methods that have been provided in HeapPage or in src/simpledb/HeapFileEncoder.java to understand the layout of pages.
You will also need to implement an Iterator over the tuples in the page, which may involve an auxiliary class or data structure.
At this point, your code should pass the unit tests in HeapPageIdTest, RecordIDTest, and HeapPageReadTest.
After you have implemented HeapPage, you will write methods for HeapFile in this lab to calculate the number of pages in a file and to read a page from the file. You will then be able to fetch tuples from a file stored on disk.
Implement the skeleton methods in:
- src/simpledb/HeapFile.java
To read a page from disk, you will first need to calculate the correct offset in the file. Hint: you will need random access to the file in order to read and write pages at arbitrary offsets. You should not call BufferPool methods when reading a page from disk.
You will also need to implement the `HeapFile.iterator()` method, which should iterate through through the tuples of each page in the HeapFile. The iterator must use the `BufferPool.getPage()` method to access pages in the `HeapFile`. This method loads the page into the buffer pool and will eventually be used (in a later lab) to implement locking-based concurrency control and recovery. Do not load the entire table into memory on the open() call -- this will cause an out of memory error for very large tables.
At this point, your code should pass the unit tests in HeapFileReadTest.
Operators are responsible for the actual execution of the query plan. They implement the operations of the relational algebra. In SimpleDB, operators are iterator based; each operator implements the DbIterator interface.
Operators are connected together into a plan by passing lower-level operators into the constructors of higher-level operators, i.e., by 'chaining them together.' Special access method operators at the leaves of the plan are responsible for reading data from the disk (and hence do not have any operators below them).
At the top of the plan, the program interacting with SimpleDB simply calls getNext on the root operator; this operator then calls getNext on its children, and so on, until these leaf operators are called. They fetch tuples from disk and pass them up the tree (as return arguments to getNext); tuples propagate up the plan in this way until they are output at the root or combined or rejected by another operator in the plan.
For this lab, you will only need to implement one SimpleDB operator.
Implement the skeleton methods in:
- src/simpledb/SeqScan.java
This operator sequentially scans all of the tuples from the pages of the table specified by the tableid in the constructor. This operator should access tuples through the DbFile.iterator() method.
At this point, you should be able to complete the ScanTest system test. Good work!
You will fill in other operators in subsequent labs.
The purpose of this section is to illustrate how these various components are connected together to process a simple query.
Suppose you have a data file, "some_data_file.txt", with the following contents:
1,1,1
2,2,2
3,4,4
You can convert this into a binary file that SimpleDB can query as follows:
```java -jar dist/simpledb.jar convert some_data_file.txt 3```
Here, the argument "3" tells conver that the input has 3 columns.
The following code implements a simple selection query over this file. This code is equivalent to the SQL statement `SELECT * FROM some_data_file`.
package simpledb;
import java.io.*;
public class test {
public static void main(String[] argv) {
// construct a 3-column table schema
Type types[] = new Type[]{ Type.INT_TYPE, Type.INT_TYPE, Type.INT_TYPE };
String names[] = new String[]{ "field0", "field1", "field2" };
TupleDesc descriptor = new TupleDesc(types, names);
// create the table, associate it with some_data_file.dat
// and tell the catalog about the schema of this table.
HeapFile table1 = new HeapFile(new File("some_data_file.dat"), descriptor);
Database.getCatalog().addTable(table1, "test");
// construct the query: we use a simple SeqScan, which spoonfeeds
// tuples via its iterator.
TransactionId tid = new TransactionId();
SeqScan f = new SeqScan(tid, table1.getId());
try {
// and run it
f.open();
while (f.hasNext()) {
Tuple tup = f.next();
System.out.println(tup);
}
f.close();
Database.getBufferPool().transactionComplete(tid);
} catch (Exception e) {
System.out.println ("Exception : " + e);
}
}
}
The table we create has three integer fields. To express this, we create a TupleDesc object and pass it an array of Type objects, and optionally an array of String field names. Once we have created this TupleDesc, we initialize a HeapFile object representing the table stored in some_data_file.dat. Once we have created the table, we add it to the catalog. If this were a database server that was already running, we would have this catalog information loaded. We need to load it explicitly to make this code self-contained.
Once we have finished initializing the database system, we create a query plan. Our plan consists only of the SeqScan operator that scans the tuples from disk. In general, these operators are instantiated with references to the appropriate table (in the case of SeqScan) or child operator (in the case of e.g. Filter). The test program then repeatedly calls hasNext and next on the SeqScan operator. As tuples are output from the SeqScan, they are printed out on the command line.
We strongly recommend you try this out as a fun end-to-end test that will help you get experience writing your own test programs for simpledb. You should create the file "test.java" in the src/simpledb directory with the code above, and place the some_data_file.dat file in the top level directory. Then run:
ant
java -classpath dist/simpledb.jar simpledb.test
Note that ant compiles test.java and generates a new jarfile that contains it.
You must submit your code (see below) as well as a short (2 pages, maximum) writeup describing your approach. This writeup should:
- Describe any design decisions you made. These may be minimal for Lab 1.
- Discuss and justify any changes you made to the API.
- Describe any missing or incomplete elements of your code.
- Describe how long you spent on the lab, and whether there was anything you found particularly difficult or confusing.
This lab should be manageable for a single person, but if you prefer to work with a partner, this is also OK. Larger groups are not allowed. Please indicate clearly who you worked with, if anyone, on your individual writeup.
You may submit your code multiple times; we will use the latest version you submit that arrives before the deadline (before 11:59 PM on the due date). Place the write-up in a file called lab1-writeup.txt, which has been created for you in the top level of your simple-db-hw directory.
You also need to explicitly add any other files you create, such as new *.java files.
The criteria for your lab being submitted on time is that your code must be tagged and pushed by the date and time. This means that if one of the TAs or the instructor were to open up GitHub, they would be able to see your solutions on the GitHub web page.
Just because your code has been commited on your local machine does not mean that it has been submitted; it needs to be on GitHub.
There is a bash script turnInLab1.sh in the root level directory of simple-db-hw that commits your changes, deletes any prior tag for the current lab, tags the current commit, and pushes the branch and tag to github. If you are using Linux or Mac OSX, you should be able to run the following:
$ ./turnInLab1.shYou should see something like the following output:
$ ./turnInLab1.sh
error: tag 'lab1submit' not found.
remote: warning: Deleting a non-existent ref.
To git@github.com:MIT-DB-Class/homework-solns-2018-<athena username>.git
- [deleted] lab1submit
[master 7a26701] Lab 1
1 file changed, 0 insertions(+), 0 deletions(-)
create mode 100644 aaa
Counting objects: 3, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (3/3), done.
Writing objects: 100% (3/3), 353 bytes | 0 bytes/s, done.
Total 3 (delta 1), reused 0 (delta 0)
remote: Resolving deltas: 100% (1/1), completed with 1 local objects.
To git@github.com:MIT-DB-Class/homework-solns-2018-<athena username>.git
069856c..7a26701 master -> master
* [new tag] lab1submit -> lab1submitIf the above command worked for you, you can skip to item 6 below. If not, submit your solutions for lab 1 as follows:
-
Look at your current repository status.
$ git status
-
Add and commit your code changes (if they aren't already added and commited).
$ git commit -a -m 'Lab 1' -
Delete any prior local and remote tag (this will return an error if you have not tagged previously; this allows you to submit multiple times)
$ git tag -d lab1submit $ git push origin :refs/tags/lab1submit
-
Tag your last commit as the lab to be graded
$ git tag -a lab1submit -m 'submit lab 1' -
This is the most important part: push your solutions to GitHub.
$ git push origin master --tags
-
The last thing that we strongly recommend you do is to go to the [MIT-DB-Class] organization page on GitHub to make sure that we can see your solutions.
Just navigate to your repository and check that your latest commits are on GitHub. You should also be able to check
https://github.com/MIT-DB-Class/homework-solns-2018-<athena username>/tree/lab1submit
Git is a distributed version control system. This means everything operates offline until you run git pull or git push. This is a great feature.
The bad thing is that you may forget to git push your changes. This is why we strongly, strongly suggest that you check GitHub to be sure that what you want us to see matches up with what you expect.
Please submit (friendly!) bug reports to 6.830-staff@mit.edu. When you do, please try to include:
- A description of the bug.
- A .java file we can drop in the test/simpledb directory, compile, and run.
- A .txt file with the data that reproduces the bug. We should be able to convert it to a .dat file using HeapFileEncoder.
If you are the first person to report a particular bug in the code, we will give you a candy bar!
75% of your grade will be based on whether or not your code passes the system test suite we will run over it. These tests will be a superset of the tests we have provided. Before handing in your code, you should make sure it produces no errors (passes all of the tests) from both ant test and ant systemtest.
Important: before testing, we will replace your build.xml and the entire contents of the test directory with our version of these files. This means you cannot change the format of .dat files! You should also be careful changing our APIs. You should test that your code compiles the unmodified tests.
In other words, we will pull your repo, replace the files mentioned above, compile it, and then grade it. It will look roughly like this:
[replace build.xml and test]
$ git checkout -- build.xml test\
$ ant test
$ ant systemtest
[additional tests]
If any of these commands fail, we`ll be unhappy, and, therefore, so will your grade.
An additional 25% of your grade will be based on the quality of your writeup and our subjective evaluation of your code.
We`ve had a lot of fun designing this assignment, and we hope you enjoy hacking on it!