MINIFICPP-366 Added docs for expression language
This closes #249.
Signed-off-by: Aldrin Piri <aldrin@apache.org>
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+<!--
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+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You 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.
+-->
+# MiNiFi - C++ Expression Language
+
+Apache NiFi - MiNiFi - C++ supports a subset of the [Apache NiFi Expression
+Language](https://nifi.apache.org/docs/nifi-docs/html/expression-language-guide.html)
+(EL). EL is a tiny DSL enabling processor property values to be computed
+dynamically according to contextual information such as FlowFile attributes.
+Dynamic values may be manipulated by a number of functions supported by EL,
+including boolean logic, string manipulation, encoding/decoding, searching,
+mathematical operators, date manipulation, type coercion, and more.
+Processors/properties supporting EL are marked in the [processors
+documentation](PROCESSORS.md).
+
+## Overview
+
+All data in Apache NiFi is represented by an abstraction called a FlowFile. A
+FlowFile comprises two major pieces: content and attributes. The content
+portion of the FlowFile represents the data on which to operate. For instance,
+if a file is picked up from a local file system using the GetFile Processor,
+the contents of the file will become the contents of the FlowFile.
+
+The attributes portion of the FlowFile represents information about the data
+itself, or metadata. Attributes are key-value pairs that represent what is
+known about the data as well as information that is useful for routing and
+processing the data appropriately. Keeping with the example of a file that is
+picked up from a local file system, the FlowFile would have an attribute called
+`filename` that reflected the name of the file on the file system.
+Additionally, the FlowFile will have a `path` attribute that reflects the
+directory on the file system that this file lived in. The FlowFile will also
+have an attribute named `uuid`, which is a unique identifier for this FlowFile.
+For complete listing of the core attributes check out the FlowFile section of
+the Apache NiFi Developer’s Guide.
+
+However, placing these attributes on a FlowFile do not provide much benefit if
+the user is unable to make use of them. The NiFi Expression Language provides
+the ability to reference these attributes, compare them to other values, and
+manipulate their values.
+
+## Structure of a NiFi Expression
+
+The NiFi Expression Language always begins with the start delimiter `${` and
+ends with the end delimiter `}`. Between the start and end delimiters is the
+text of the Expression itself. In its most basic form, the Expression can
+consist of just an attribute name. For example, `${filename}` will return the
+value of the `filename` attribute.
+
+In a slightly more complex example, we can instead return a manipulation of
+this value. We can, for example, return an all upper-case version of the
+filename by calling the `toUpper` function: `${filename:toUpper()}`. In this
+case, we reference the `filename` attribute and then manipulate this value by
+using the `toUpper` function. A function call consists of 5 elements. First,
+there is a function call delimiter `:`. Second is the name of the function --in
+this case, `toUpper`. Next is an open parenthesis (`(`), followed by the
+function arguments. The arguments necessary are dependent upon which function
+is being called. In this example, we are using the `toUpper` function, which
+does not have any arguments, so this element is omitted. Finally, the closing
+parenthesis (`)`) indicates the end of the function call. There are many
+different functions that are supported by the Expression Language to achieve
+many different goals. Some functions provide String (text) manipulation, such
+as the `toUpper` function. Others, such as the equals and matches functions,
+provide comparison functionality. Functions also exist for manipulating dates
+and times and for performing mathematical operations. Each of these functions
+is described below, in the Functions section, with an explanation of what the
+function does, the arguments that it requires, and the type of information that
+it returns.
+
+When we perform a function call on an attribute, as above, we refer to the
+attribute as the subject of the function, as the attribute is the entity on
+which the function is operating. We can then chain together multiple function
+calls, where the return value of the first function becomes the subject of the
+second function and its return value becomes the subject of the third function
+and so on. Continuing with our example, we can chain together multiple
+functions by using an expression similar to
+`${filename:toUpper():equals('HELLO.TXT')}`. There is no limit to the number
+of functions that can be chained together.
+
+Any FlowFile attribute can be referenced using the Expression Language.
+However, if the attribute name contains a special character, the attribute
+name must be escaped by quoting it. The following characters are each
+considered special characters:
+
+- `$` (dollar sign)
+- `|` (pipe)
+- `{` (open brace)
+- `}` (close brace)
+- `(` (open parenthesis)
+- `)` (close parenthesis)
+- `[` (open bracket)
+- `]` (close bracket)
+- `,` (comma)
+- `:` (colon)
+- `;` (semicolon)
+- `/` (forward slash)
+- `*` (asterisk)
+- `'` (single quote)
+- ` ` (space)
+- `\t` (tab)
+- `\r` (carriage return)
+- `\n` (new-line)
+
+Additionally, a number is considered a special character if it is the first
+character of the attribute name. If any of these special characters is present
+in an attribute is quoted by using either single or double quotes. The
+Expression Language allows single quotes and double quotes to be used
+interchangeably. For example, the following can be used to escape an attribute
+named my attribute: `${"my attribute"}` or `${'my attribute'}`.
+
+In this example, the value to be returned is the value of the "my attribute"
+value, if it exists. If that attribute does not exist, the Expression Language
+will then look for a System Environment Variable named "my attribute." Finally,
+if none of these exists, the Expression Language will return a null value.
+
+There also exist some functions that expect to have no subject. These functions
+are invoked simply by calling the function at the beginning of the Expression,
+such as `${hostname()}`. These functions can then be changed together, as well.
+For example, `${hostname():toUpper()}`. Attempting to evaluate the function with
+subject will result in an error. In the Functions section below, these
+functions will clearly indicate in their descriptions that they do not require
+a subject.
+
+Often times, we will need to compare the values of two different attributes to
+each other. We are able to accomplish this by using embedded Expressions. We
+can, for example, check if the filename attribute is the same as the uuid
+attribute: `${filename:equals( ${uuid} )}`. Notice here, also, that we have a
+space between the opening parenthesis for the equals method and the embedded
+Expression. This is not necessary and does not affect how the Expression is
+evaluated in any way. Rather, it is intended to make the Expression easier to
+read. White space is ignored by the Expression Language between delimiters.
+Therefore, we can use the Expression `${ filename : equals(${ uuid}) }` or
+`${filename:equals(${uuid})}` and both Expressions mean the same thing. We
+cannot, however, use `${file name:equals(${uuid})}`, because this results in
+file and name being interpreted as different tokens, rather than a single
+token, filename.
+
+## Supported Features
+
+### String Manipulation
+
+- [`toUpper`](#toupper)
+- [`toLower`](#tolower)
+- [`substring`](#substring)
+- [`substringBefore`](#substringbefore)
+- [`substringBeforeLast`](#substringbeforelast)
+- [`substringAfter`](#substringafter)
+- [`substringAfterLast`](#substringafterlast)
+- [`replace`](#replace)
+- [`replaceFirst`](#replacefirst)
+- [`replaceAll`](#replaceall)
+- [`replaceNull`](#replacenull)
+- [`replaceEmpty`](#replaceempty)
+
+### Mathematical Operations and Numeric Manipulation
+
+- [`plus`](#plus)
+- [`minus`](#minus)
+- [`multiply`](#multiply)
+- [`divide`](#divide)
+- [`mod`](#mod)
+- [`toRadix`](#toradix)
+- [`fromRadix`](#fromradix)
+- [`random`](#random)
+
+## Planned Features
+
+### String Manipulation
+
+- `trim`
+- `getDelimitedField`
+- `append`
+- `prepend`
+- `length`
+
+### Boolean Logic
+
+- `isNull`
+- `notNull`
+- `isEmpty`
+- `equals`
+- `equalsIgnoreCase`
+- `gt`
+- `ge`
+- `lt`
+- `le`
+- `and`
+- `or`
+- `not`
+- `ifElse`
+
+### Encode/Decode Functions
+
+- `escapeJson`
+- `escapeXml`
+- `escapeCsv`
+- `escapeHtml3`
+- `escapeHtml4`
+- `unescapeJson`
+- `unescapeXml`
+- `unescapeCsv`
+- `unescapeHtml3`
+- `unescapeHtml4`
+- `urlEncode`
+- `urlDecode`
+- `base64Encode`
+- `base64Decode`
+
+### Encode/Decode Functions
+
+- `escapeJson`
+- `escapeXml`
+- `escapeCsv`
+- `escapeHtml3`
+- `escapeHtml4`
+- `unescapeJson`
+- `unescapeXml`
+- `unescapeCsv`
+- `unescapeHtml3`
+- `unescapeHtml4`
+- `urlEncode`
+- `urlDecode`
+- `base64Encode`
+- `base64Decode`
+
+### Date Manipulation
+
+- `format`
+- `toDate`
+- `now`
+
+### Subjectless Functions
+
+- `ip`
+- `hostname`
+- `UUID`
+- `nextInt`
+- `literal`
+- `getStateValue`
+
+### Evaluating Multiple Attributes
+
+- `anyAttribute`
+- `allAttributes`
+- `anyMatchingAttribute`
+- `allMatchingAttributes`
+- `anyDelineatedValue`
+- `allDelineatedValues`
+- `join`
+- `count`
+
+## Unsupported Features
+
+The following EL features are currently not supported, and no support is
+planned due to language/environment (Java vs. C++) differences:
+
+### Mathematical Operations and Numeric Manipulation
+
+- `math `
+
+## String Manipulation
+
+Each of the following functions manipulates a String in some way.
+
+### toUpper
+
+**Description**: This function converts the Subject into an all upper-case
+String. Said another way, it replaces any lowercase letter with the uppercase
+equivalent.
+
+**Subject Type**: String
+
+**Arguments**: No arguments
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute is `abc123.txt`, then the Expression
+`${filename:toUpper()}` will return `ABC123.TXT`
+
+### toLower
+
+**Description**: This function converts the Subject into an all lower-case
+String. Said another way, it replaces any uppercase letter with the lowercase
+equivalent.
+
+**Subject Type**: String
+
+**Arguments**: No arguments
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute is `ABC123.TXT`, then the Expression
+`${filename:toLower()}` will return `abc123.txt`
+
+### substring
+
+**Description**: Returns a portion of the Subject, given a starting index and
+an optional ending index. If the ending index is not supplied, it will return
+the portion of the Subject starting at the given 'start index' and ending at
+the end of the Subject value.
+
+The starting index and ending index are zero-based. That is, the first
+character is referenced by using the value 0, not 1.
+
+If either the starting index is or the ending index is not a number, this
+function call will result in an error.
+
+If the starting index is larger than the ending index, this function call will
+result in an error.
+
+If the starting index or the ending index is greater than the length of the
+Subject or has a value less than 0, this function call will result in an error.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| starting index | The 0-based index of the first character to capture (inclusive) |
+| ending index | The 0-based index of the last character to capture (exclusive) |
+
+**Return Type**: String
+
+**Examples**:
+
+If we have an attribute named `filename` with the value `a brand new
+filename.txt`, then the following Expressions will result in the following
+values:
+
+| Expression | Value |
+| - | - |
+| `${filename:substring(0,1)}` | a |
+| `${filename:substring(2)}` | brand new filename.txt |
+| `${filename:substring(12)}` | filename.txt |
+| `${filename:substring( ${filename:length():minus(2)} )}` | xt |
+
+### substringBefore
+
+**Description**: Returns a portion of the Subject, starting with the first
+character of the Subject and ending with the character immediately before the
+first occurrence of the argument. If the argument is not present in the
+Subject, the entire Subject will be returned.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| value | The String to search for in the Subject |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will result in the following
+values:
+
+| Expression | Value |
+| - | - |
+| `${filename:substringBefore('.')}` | a brand new filename |
+| `${filename:substringBefore(' ')}` | a |
+| `${filename:substringBefore(' n')}` | a brand |
+| `${filename:substringBefore('missing')}` | a brand new filename.txt |
+
+### substringBeforeLast
+
+**Description**: Returns a portion of the Subject, starting with the first
+character of the Subject and ending with the character immediately before the
+last occurrence of the argument. If the argument is not present in the Subject,
+the entire Subject will be returned.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| value | The String to search for in the Subject |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will result in the following
+values:
+
+| Expression | Value |
+| - | - |
+| `${filename:substringBeforeLast('.')}` | a brand new filename |
+| `${filename:substringBeforeLast(' ')}` | a brand new |
+| `${filename:substringBeforeLast(' n')}` | a brand |
+| `${filename:substringBeforeLast('missing')}` | a brand new filename.txt |
+
+### substringAfter
+
+**Description**: Returns a portion of the Subject, starting with the character
+immediately after the first occurrence of the argument and extending to the end
+of the Subject. If the argument is not present in the Subject, the entire
+Subject will be returned.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| value | The String to search for in the Subject |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will result in the following
+values:
+
+| Expression | Value |
+| - | - |
+| `${filename:substringAfter('.')}` | txt |
+| `${filename:substringAfter(' ')}` | brand new filename.txt |
+| `${filename:substringAfter(' n')}` | ew filename.txt |
+| `${filename:substringAfter('missing')}` | a brand new filename.txt |
+
+### substringAfterLast
+
+**Description**: Returns a portion of the Subject, starting with the character
+immediately after the last occurrence of the argument and extending to the end
+of the Subject. If the argument is not present in the Subject, the entire
+Subject will be returned.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| value | The String to search for in the Subject |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will result in the following
+values:
+
+| Expression | Value |
+| - | - |
+| `${filename:substringAfterLast('.')}` | txt |
+| `${filename:substringAfterLast(' ')}` | filename.txt |
+| `${filename:substringAfterLast(' n')}` | ew filename.txt |
+| `${filename:substringAfterLast('missing')}` | a brand new filename.txt |
+
+### replace
+
+**Description**: Replaces all occurrences of one literal String within the Subject
+with another String.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Search String | The String to find within the Subject |
+| Replacement | The value to replace Search String with |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will provide the following
+results:
+
+| Expression | Value |
+| - | - |
+| `${filename:replace('.', '_')}` | a brand new filename_txt |
+| `${filename:replace(' ', '.')}` | a.brand.new.filename.txt |
+| `${filename:replace('XYZ', 'ZZZ')}` | a brand new filename.txt |
+| `${filename:replace('filename', 'book')}` | a brand new book.txt |
+
+### replaceFirst
+
+**Description**: Replaces the first occurrence of one literal String or regular
+expression within the Subject with another String.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Search String | The String (literal or regular expression pattern) to find within the Subject |
+| Replacement | The value to replace Search String with |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will provide the following
+results:
+
+| Expression | Value |
+| - | - |
+| `${filename:replaceFirst('a', 'the')}` | the brand new filename.txt |
+| `${filename:replaceFirst('[br]', 'g')}` | a grand new filename.txt |
+| `${filename:replaceFirst('XYZ', 'ZZZ')}` | a brand new filename.txt |
+| `${filename:replaceFirst('\w{8}', 'book')}` | a brand new book.txt |
+
+### replaceAll
+
+**Description**: The replaceAll function takes two String arguments: a literal
+String or Regular Expression (NiFi uses the Java Pattern syntax), and a
+replacement string. The return value is the result of substituting the
+replacement string for all patterns within the Subject that match the Regular
+Expression.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Regex | he Regular Expression (in Java syntax) to match in the Subject |
+| Replacement | The value to use for replacing matches in the Subject. If the regular expression argument uses Capturing Groups, back references are allowed in the replacement. |
+
+**Return Type**: String
+
+**Examples**: If the `filename` attribute has the value `a brand new
+filename.txt`, then the following Expressions will provide the following
+results:
+
+| Expression | Value |
+| - | - |
+| `${filename:replaceAll('\..*', '')}` | a brand new filename |
+| `${filename:replaceAll('a brand (new)', '$1')}` | new filename.txt |
+| `${filename:replaceAll('XYZ', 'ZZZ')}` | a brand new filename.txt |
+| `${filename:replaceAll('brand (new)', 'somewhat $1')}` | a somewhat new filename.txt |
+
+### replaceNull
+
+**Description**: The replaceNull function returns the argument if the Subject is
+null. Otherwise, returns the Subject.
+
+**Subject Type**: Any
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Replacement | The value to return if the Subject is null. |
+
+**Return Type**: Type of Subject if Subject is not null; else, type of Argument
+
+**Examples**: If the attribute `filename` has the value `a brand new filename.txt` and the attribute `hello` does not exist, then the Expression `${filename:replaceNull('abc')}` will return `a brand new filename.txt`, while `${hello:replaceNull('abc')}` will return `abc`.
+
+### replaceEmpty
+
+**Description**: The replaceEmpty function returns the argument if the Subject is
+null or if the Subject consists only of white space (new line, carriage return,
+tab, space). Otherwise, returns the Subject.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Replacement | The value to return if the Subject is null or empty. |
+
+**Return Type**: String
+
+**Examples**: If the attribute `filename` has the value `a brand new
+filename.txt` and the attribute `hello` has the value ` `, then the Expression
+`${filename:replaceEmpty('abc')}` will return `a brand new filename.txt`, while
+`${hello:replaceEmpty('abc')}` will return `abc`.
+
+## Mathematical Operations and Numeric Manipulation
+
+For those functions that support Decimal and Number (whole number) types, the
+return value type depends on the input types. If either the subject or argument
+are a Decimal then the result will be a Decimal. If both values are Numbers
+then the result will be a Number. This includes Divide. This is to preserve
+backwards compatibility and to not force rounding errors.
+
+### plus
+
+**Description**: Adds a numeric value to the Subject. If either the argument or the
+Subject cannot be coerced into a Number, returns null.
+
+**Subject Type**: Number or Decimal
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Operand | The value to add to the Subject |
+
+**Return Type**: Number or Decimal (depending on input types)
+
+**Examples**: If the `fileSize` attribute has a value of 100, then the
+Expression `${fileSize:plus(1000)}` will return the value 1100.
+
+### minus
+
+**Description**: Subtracts a numeric value from the Subject.
+
+**Subject Type**: Number or Decimal
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Operand | The value to subtract from the Subject |
+
+**Return Type**: Number or Decimal (depending on input types)
+
+**Examples**: If the `fileSize` attribute has a value of 100, then the
+Expression `${fileSize:minus(100)}` will return the value 0.
+
+### multiply
+
+**Description**: Multiplies a numeric value by the Subject and returns the product.
+
+**Subject Type**: Number or Decimal
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Operand | The value to multiple the Subject by |
+
+**Return Type**: Number or Decimal (depending on input types)
+
+**Examples**: If the `fileSize` attribute has a value of 100, then the
+Expression `${fileSize:multiply(1024)}` will return the value 102400.
+
+### divide
+
+**Description**: Divides the Subject by a numeric value and returns the result.
+
+**Subject Type**: Number or Decimal
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Operand | The value to divide the Subject by |
+
+**Return Type**: Number or Decimal (depending on input types)
+
+**Examples**: If the `fileSize` attribute has a value of 100, then the
+Expression `${fileSize:divide(12)}` will return the value 8.
+
+### mod
+
+**Description**: Performs a modular division of the Subject by the argument. That
+is, this function will divide the Subject by the value of the argument and
+return not the quotient but rather the remainder.
+
+**Subject Type**: Number or Decimal
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Operand | The value to divide the Subject by |
+
+**Return Type**: Number or Decimal (depending on input types)
+
+**Examples**: If the `fileSize` attribute has a value of 100, then the
+Expression `${fileSize:mod(12)}` will return the value 4.
+
+### toRadix
+
+**Description**: Converts the Subject from a Base 10 number to a
+different Radix (or number base). An optional second argument can be used to
+indicate the minimum number of characters to be used. If the converted value
+has fewer than this number of characters, the number will be padded with
+leading zeroes.
+
+If a decimal is passed as the subject, it will first be converted to a whole
+number and then processed.
+
+**Subject Type**: Number
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Desired Base | A Number between 2 and 36 (inclusive) |
+| Padding | Optional argument that specifies the minimum number of characters in the converted output |
+
+**Return Type**: String
+
+**Examples**: If the `fileSize` attributes has a value of 1024, then the
+following Expressions will yield the following results:
+
+| Expression | Value |
+| - | - |
+| `${fileSize:toRadix(10)}` | 1024 |
+| `${fileSize:toRadix(10, 1)}` | 1024 |
+| `${fileSize:toRadix(10, 8)}` | 00001024 |
+| `${fileSize:toRadix(16)}` | 400 |
+| `${fileSize:toRadix(16, 8)}` | 00000400 |
+| `${fileSize:toRadix(2)}` | 10000000000 |
+| `${fileSize:toRadix(2, 16)}` | 0000010000000000 |
+
+### fromRadix
+
+**Description**: Converts the Subject from a specified Radix (or
+number base) to a base ten whole number. The subject will converted as is,
+without interpretation, and all characters must be valid for the base being
+converted from. For example converting "0xFF" from hex will not work due to "x"
+being a invalid hex character.
+
+If a decimal is passed as the subject, it will first be converted to a whole
+number and then processed.
+
+**Subject Type**: String
+
+**Arguments**:
+
+| Argument | Description |
+| - | - |
+| Subject Base | A Number between 2 and 36 (inclusive) |
+
+**Return Type**: Number
+
+**Examples**: If the `fileSize` attributes has a value of 1234A, then the
+following Expressions will yield the following results:
+
+| Expression | Value |
+| - | - |
+| `${fileSize:fromRadix(11)}` | 17720 |
+| `${fileSize:fromRadix(16)}` | 74570 |
+| `${fileSize:fromRadix(20)}` | 177290 |
+
+### random
+
+**Description**: Returns a random whole number (0 to 2^63 - 1) using an insecure
+random number generator.
+
+**Subject Type**: No subject
+
+**Arguments**: No arguments
+
+**Return Type**: Number
+
+**Examples**: `${random():mod(10):plus(1)}` returns random number between 1 and 10 inclusive.
diff --git a/README.md b/README.md
index 2c6fd41..6a7e584 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,7 @@
Apache NiFi - MiNiFi C++ is a complementary data collection approach that supplements the core tenets of [NiFi](http://nifi.apache.org/) in dataflow management, focusing on the collection of data at the source of its creation. The C++ implementation is an additional implementation to the one in Java with the aim of an even smaller resource footprint.
-Specific goals for MiNiFi are comprised of:
+Specific goals for MiNiFi comprise:
- small and lightweight footprint
- central management of agents
- generation of data provenance
@@ -42,6 +42,10 @@
Perspectives of the role of MiNiFi should be from the perspective of the agent acting immediately at, or directly adjacent to, source sensors, systems, or servers.
+### Expression Language
+
+A subset of the Apache NiFi [Expression Language](EXPRESSIONS.md) is supported.
+
### Processors
MiNiFi - C++ supports the following processors:
