diff --git a/books.dtd b/books.dtd
new file mode 100644
index 0000000..6a4c67b
--- /dev/null
+++ b/books.dtd
@@ -0,0 +1,13 @@
+<!ELEMENT bookstore (book*)>
+<!ELEMENT book (title, author+, year, price)>
+<!ATTLIST book
+category CDATA #REQUIRED
+cover (hardback|paperback) #IMPLIED
+>
+<!ELEMENT title (#PCDATA)>
+<!ATTLIST title
+lang CDATA "en"
+>
+<!ELEMENT author (#PCDATA)>
+<!ELEMENT year (#PCDATA)>
+<!ELEMENT price (#PCDATA)>
diff --git a/books.xml b/books.xml
index 49f0348..1c901ae 100644
--- a/books.xml
+++ b/books.xml
@@ -1,30 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE student SYSTEM "books.dtd">
 <bookstore>
-  <book category="cooking">
-    <title lang="en">Everyday Italian</title>
-    <author>Giada De Laurentiis</author>
-    <year>2005</year>
-    <price>30.00</price>
-  </book>
-  <book category="children">
-    <title lang="en">Harry Potter</title>
-    <author>J K. Rowling</author>
-    <year>2005</year>
-    <price>29.99</price>
-  </book>
-  <book category="web">
-    <title lang="en">XQuery Kick Start</title>
-    <author>James McGovern</author>
-    <author>Per Bothner</author>
-    <author>Kurt Cagle</author>
-    <author>James Linn</author>
-    <author>Vaidyanathan Nagarajan</author>
-    <year>2003</year>
-    <price>49.99</price>
-  </book>
-  <book category="web" cover="paperback">
-    <title lang="en">Learning XML</title>
-    <author>Erik T. Ray</author>
-    <year>2003</year>
-    <price>39.95</price>
-  </book>
+<book category="cooking">
+<title lang="en">Everyday Italian</title>
+<author>Giada De Laurentiis</author>
+<year>2005</year>
+<price>30.00</price>
+</book>
+<book category="children">
+<title lang="en">Harry Potter</title>
+<author>J K. Rowling</author>
+<year>2005</year>
+<price>29.99</price>
+</book>
+<book category="web">
+<title lang="en">XQuery Kick Start</title>
+<author>James McGovern</author>
+<author>Per Bothner</author>
+<author>Kurt Cagle</author>
+<author>James Linn</author>
+<author>Vaidyanathan Nagarajan</author>
+<year>2003</year>
+<price>49.99</price>
+</book>
+<book category="web" cover="paperback">
+<title lang="en">Learning XML</title>
+<author>Erik T. Ray</author>
+<year>2003</year>
+<price>39.95</price>
+</book>
 </bookstore>
diff --git a/books.xsd b/books.xsd
new file mode 100644
index 0000000..1c0c19d
--- /dev/null
+++ b/books.xsd
@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
+
+<xs:element name="bookstore" type="bookstoreType"/>
+
+<xs:complexType name="bookstoreType">
+	<xs:sequence>
+		<xs:element name="book" type="bookType" minOccurs="0" maxOccurs="unbounded"/>
+	</xs:sequence>
+</xs:complexType>
+<xs:complexType name="bookType">
+	
+	<xs:sequence>
+		<xs:element name="title">
+			<xs:complexType>
+				<xs:simpleContent>
+					<xs:restriction base="titleType">
+						<xs:minLength value="2"/>
+						<xs:maxLength value="30"/>
+					</xs:restriction>
+				</xs:simpleContent>
+			</xs:complexType>
+		</xs:element>
+			<xs:element name="author" minOccurs="1" maxOccurs="unbounded">
+				<xs:simpleType>
+					<xs:restriction base="xs:string">
+						<xs:minLength value="2"/>
+						<xs:maxLength value="30"/>
+					</xs:restriction>
+				</xs:simpleType>
+		</xs:element>
+			<xs:element name="year">
+			<xs:simpleType>
+				<xs:restriction base="xs:integer">
+					<xs:minInclusive value="1900"/>
+					<xs:maxInclusive value="2014"/>
+				</xs:restriction>
+			</xs:simpleType>
+		</xs:element>
+<xs:element name="price">
+	<xs:simpleType>
+		<xs:restriction base="xs:decimal">
+			<xs:minInclusive value="0"/>
+		</xs:restriction>
+	</xs:simpleType>
+</xs:element>
+</xs:sequence>
+<xs:attribute name="category" type="xs:string" use="required"/>
+<xs:attribute name="cover" use="optional">
+<xs:simpleType>
+	<xs:restriction base="xs:string">
+	<xs:enumeration value="hardback"/>
+	<xs:enumeration value="paperback"/>
+</xs:restriction>
+</xs:simpleType>
+</xs:attribute>
+</xs:complexType>
+<!-- type for title to define attribute-->
+<xs:complexType name="titleType">
+	<xs:simpleContent>
+		<xs:extension base="xs:string">
+			<xs:attribute name="lang" use="required">
+				<xs:simpleType>
+					<xs:restriction base="xs:string">
+					<xs:length value="2"/>
+					</xs:restriction>
+				</xs:simpleType>
+			</xs:attribute>
+		</xs:extension>
+	</xs:simpleContent>
+</xs:complexType>
+</xs:schema>
diff --git a/student.dtd b/student.dtd
index 3613239..f8624c8 100644
--- a/student.dtd
+++ b/student.dtd
@@ -1 +1,5 @@
-<!ELEMENT student EMPTY>
+<!ELEMENT student (#PCDATA)>
+<!ATTLIST student 
+	fullname CDATA #REQUIRED
+	group (К6-361|К6-362) #REQUIRED
+>
diff --git a/student.xml b/student.xml
new file mode 100644
index 0000000..6991a9a
--- /dev/null
+++ b/student.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE student SYSTEM "student.dtd">
+<student fullname = "Dzhumaylo Evgeny" group = "К6-362">
+</student>
diff --git a/task16 b/task16
new file mode 100644
index 0000000..52639a1
--- /dev/null
+++ b/task16
@@ -0,0 +1 @@
+//book
diff --git a/task17 b/task17
new file mode 100644
index 0000000..f582071
--- /dev/null
+++ b/task17
@@ -0,0 +1 @@
+//book[@cover]
diff --git a/task18 b/task18
new file mode 100644
index 0000000..ed203f4
--- /dev/null
+++ b/task18
@@ -0,0 +1 @@
+//book[child::year=2003]
diff --git a/task19 b/task19
new file mode 100644
index 0000000..e9e2c20
--- /dev/null
+++ b/task19
@@ -0,0 +1 @@
+//book[child::price >= 30 and child::price < 40]
diff --git a/task20.xsl b/task20.xsl
new file mode 100644
index 0000000..0f33a14
--- /dev/null
+++ b/task20.xsl
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+
+<xsl:output method="text"/>
+
+<xsl:template match="/">
+	<html>
+		<body>
+			<xsl:for-each select="//book">
+				<xsl:value-of select="title"/> 					<xsl:text>&#xa;</xsl:text>
+			</xsl:for-each>
+		</body>
+	</html>
+</xsl:template>
+</xsl:stylesheet>
diff --git a/task21.xsl b/task21.xsl
new file mode 100644
index 0000000..043407c
--- /dev/null
+++ b/task21.xsl
@@ -0,0 +1,18 @@
+
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+
+<xsl:output method="text"/>
+
+<xsl:template match="/">
+
+	<html>
+		<body>
+			<xsl:for-each select="//book">
+				<xsl:sort select="price"/>
+				<xsl:value-of select="title"/> 					<xsl:text>&#xa;</xsl:text>
+			</xsl:for-each>
+		</body>
+	</html>
+</xsl:template>
+</xsl:stylesheet>
diff --git a/task22.xsl b/task22.xsl
new file mode 100644
index 0000000..c706928
--- /dev/null
+++ b/task22.xsl
@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+<xsl:output method="text"/>
+
+<xsl:template match="/">
+
+	<html>
+		<body>
+			<xsl:for-each select="//book">
+			<xsl:value-of select="title"/>
+			<xsl:if test="count(author) &gt; 1">
+				<xsl:text>*</xsl:text>
+			</xsl:if>
+<xsl:text>&#xa;</xsl:text>
+			</xsl:for-each>
+		</body>
+	</html>
+</xsl:template>
+</xsl:stylesheet>
diff --git a/task23.xsl b/task23.xsl
new file mode 100644
index 0000000..c42f556
--- /dev/null
+++ b/task23.xsl
@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+<xsl:output method="text"/>
+
+<xsl:template match="/">
+	<html>
+		<body>
+			<xsl:for-each select="//book">
+				<xsl:value-of select="title"/>
+				<xsl:choose>
+				<xsl:when test="price &gt; 30">
+					<xsl:text>&gt;30</xsl:text>
+				</xsl:when>
+				<xsl:otherwise>
+					<xsl:choose>
+						<xsl:when test="price &lt; 30">
+							<xsl:text>&lt;30</xsl:text>
+						</xsl:when>
+						<xsl:otherwise>
+							<xsl:text>=30</xsl:text>
+						</xsl:otherwise>
+					</xsl:choose>
+				</xsl:otherwise>
+					</xsl:choose>
+					<xsl:text>&#xa;</xsl:text>
+			</xsl:for-each>
+		</body>
+	</html>
+</xsl:template>
+</xsl:stylesheet>
diff --git a/task24.xsl b/task24.xsl
new file mode 100644
index 0000000..b2443c2
--- /dev/null
+++ b/task24.xsl
@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+<xsl:output method="text"/>
+
+<xsl:template match="/">
+
+	<html>
+		<body>
+			<xsl:text>&lt;?xml version="1.0" encoding="UTF-8"?&gt;&#xa;&lt;library&gt;</xsl:text>
+			<xsl:apply-templates/>
+			<xsl:text>&lt;/library&gt;</xsl:text>
+		</body>
+	</html>
+
+</xsl:template>
+
+<xsl:template match="book">
+		<xsl:text>&lt;book title="</xsl:text><xsl:value-of select="title"/><xsl:text>" year="</xsl:text><xsl:value-of select="year"/><xsl:text>"&gt;</xsl:text>
+		<xsl:apply-templates select="author"/>
+		<xsl:text>&lt;/book&gt;</xsl:text>
+</xsl:template>
+<xsl:template match="author">
+	<xsl:text>&lt;author name="</xsl:text><xsl:value-of select="."/><xsl:text>"&gt;</xsl:text>
+	<xsl:text>&lt;/author&gt;</xsl:text>
+</xsl:template>
+</xsl:stylesheet>