diff --git a/src/JuliaFEM.jl b/src/JuliaFEM.jl
index c8d0f36..416f2a3 100644
--- a/src/JuliaFEM.jl
+++ b/src/JuliaFEM.jl
@@ -21,7 +21,7 @@ module Testing
 end
 
 include("io.jl")
-export ModelIO
+export Xdmf, h5file, xmffile, has_child, get_child, new_dataitem
 
 include("fields.jl")
 export Field, DCTI, DVTI, DCTV, DVTV, CCTI, CVTI, CCTV, CVTV, Increment
diff --git a/src/io.jl b/src/io.jl
index 977366f..9a07c0c 100644
--- a/src/io.jl
+++ b/src/io.jl
@@ -3,51 +3,168 @@
 
 using HDF5
 using LightXML
+importall LightXML
+importall Base
 
-type ModelIO
+function new_element(name::AbstractString, attrs::Dict)
+    x = new_element(name)
+    for (k, v) in attrs
+        x[k] = v
+    end
+    return x
+end
+
+function setindex!(x::XMLElement, content::Any, attr_name::AbstractString)
+    set_attribute(x, attr_name, content)
+end
+
+function haskey(x::XMLElement, key::AbstractString)
+    return has_child(x, key) || has_attribute(x, key)
+end
+
+function get_child(x::XMLElement, child_name::AbstractString)
+    '/' in child_name && return nothing
+    m = match(r"(\w+)\[(.+)\]", child_name)
+    if m != nothing
+        child_name = m[1]
+    end
+    childs = []
+    for child in child_elements(x)
+        if name(child) == child_name
+            push!(childs, child)
+        end
+    end
+    length(childs) == 0 && return nothing
+    m == nothing && return first(childs)
+    j = tryparse(Int, m[2])
+    isnull(j) || return childs[get(j)]
+    m[2] == "end" && return childs[end]
+    m2 = match(r"@(.+)=(.+)", m[2])
+    m2 == nothing && throw("Unable to parse: $(m[2])")
+    attr_name = m2[1]
+    attr_value = m2[2]
+    for child in childs
+        has_attribute(child, attr_name) || continue
+        if get_attribute(child, attr_name) == attr_value
+            return child
+        end
+    end
+    throw("Unable to parse: $(m[2])")
+end
+
+function has_child(x::XMLElement, child_name::AbstractString)
+    return get_child(x, child_name) != nothing
+end
+
+function get_attribute(x::XMLElement, attr_name::AbstractString)
+    attr = attribute(x, attr_name)
+    numeric = tryparse(Int64, attr)
+    isnull(numeric) && (numeric = tryparse(Float64, attr))
+    isnull(numeric) && return attr
+    return get(numeric)
+end
+
+function getindex(x::XMLElement, attr_name::AbstractString)
+    attr_name = strip(attr_name, '/')
+    child = get_child(x, attr_name)
+    child == nothing || return child
+    has_attribute(x, attr_name) && return get_attribute(x, attr_name)
+    if '/' in attr_name
+        items = split(attr_name, '/')
+        attr_name = first(items)
+        length(items) > 1 || throw(KeyError(attr_name))
+        haskey(x, attr_name) || throw(KeyError(attr_name))
+        path = join(items[2:end], '/')
+        new_item = getindex(x, attr_name)
+        return new_item[path]
+    else
+        throw(KeyError(attr_name))
+    end
+end
+
+function new_child(xparent::XMLElement, name::AbstractString, attrs::Dict)
+    x = new_child(xparent, name)
+    for (k, v) in attrs
+        x[k] = v
+    end
+    return x
+end
+
+function new_child(xparent::XMLElement, name::AbstractString, attrs::Pair...)
+    x = new_child(xparent, name)
+    for (k, v) in attrs
+        x[k] = v
+    end
+    return x
+end
+
+type Xdmf
     name :: AbstractString
-    xdmf :: XMLElement
+    xml :: XMLElement
+    hdf :: HDF5File
 end
 
-function ModelIO()
-    return ModelIO(tempname())
+function new_child(xdmf::Xdmf, args...; kwargs...)
+    new_child(xdmf.xml, args...; kwargs...)
 end
 
-function ModelIO(name::AbstractString)
+function read(xdmf::Xdmf, path::AbstractString)
+    result = getindex(xdmf.xml, path)
+    if endswith(path, "DataItem")
+        format = get_attribute(result, "Format")
+        @assert format == "HDF"
+        h5file, path = map(ASCIIString, split(content(result), ':'))
+        h5file = dirname(xdmf.name) * "/" * h5file
+        isfile(h5file) || throw("Xdmf: h5 file $h5file not found!")
+        return read(xdmf.hdf, path)
+    else
+        return result
+    end
+end
+
+function Xdmf()
+    return Xdmf(tempname())
+end
+
+function h5file(xdmf::Xdmf)
+    return xdmf.name*".h5"
+end
+
+function xmffile(xdmf::Xdmf)
+    return xdmf.name*".xmf"
+end
+
+function Xdmf(name::AbstractString)
     xdmf = new_element("Xdmf")
     set_attribute(xdmf, "xmlns:xi", "http://www.w3.org/2001/XInclude")
     set_attribute(xdmf, "Version", "2.1")
-    return ModelIO(name, xdmf)
+    h5file = "$name.h5"
+    flag = isfile(h5file) ? "r+" : "w"
+    hdf = h5open(h5file, flag)
+    return Xdmf(name, xdmf, hdf)
 end
 
-function h5file(mio::ModelIO)
-    return mio.name*".h5"
+function save!(xdmf::Xdmf)
+    doc = XMLDocument()
+    set_root(doc, xdmf.xml)
+    save_file(doc, xmffile(xdmf))
 end
 
-function put!{T,N}(mio::ModelIO, path::AbstractString, data::Array{T,N})
-    hdf = h5file(mio)
-    h5write(hdf, path, data)
-end
-
-function get_dataitem{T,N}(mio::ModelIO, path::AbstractString, data::Array{T,N}; format="HDF")
+function new_dataitem{T,N}(xdmf::Xdmf, path::AbstractString, data::Array{T,N}; format="HDF")
     dataitem = new_element("DataItem")
-    n, m = size(data)
-    set_attribute(dataitem, "DataType", "$T")
-    set_attribute(dataitem, "Dimensions", "$n $m")
+    datatype = replace("$T", "64", "")
+    dimensions = join(size(data), " ")
+    set_attribute(dataitem, "DataType", datatype)
+    set_attribute(dataitem, "Dimensions", dimensions)
     set_attribute(dataitem, "Format", format)
     if format == "HDF"
-        hdf = basename(h5file(mio))
+        hdf = basename(h5file(xdmf))
+        if !exists(xdmf.hdf, path)
+            write(xdmf.hdf, path, data)
+        end
         add_text(dataitem, "$hdf:$path")
+    elseif format == "XML"
+        add_text(dataitem, strip(string(data), ['[', ']']))
     end
     return dataitem
 end
-
-function get(mio::ModelIO, path::AbstractString)
-    h5read(mio.name*".h5", path)
-end
-
-function save!(mio::ModelIO)
-    doc = XMLDocument()
-    set_root(doc, mio.xdmf)
-    save_file(doc, mio.name*".xmf")
-end
diff --git a/src/postprocess_utils.jl b/src/postprocess_utils.jl
index 70d51b3..a861c62 100644
--- a/src/postprocess_utils.jl
+++ b/src/postprocess_utils.jl
@@ -246,9 +246,12 @@ end
 
 function call(solver::Solver, ::Type{DataFrame}, field_name::AbstractString,
               abbreviation::Symbol, time::Float64=0.0)
-    u = Dict()
-    for problem in get_problems(solver)
-        u = merge(u, problem(field_name, time))
+    fields = [problem(field_name, time) for problem in get_problems(solver)]
+    fields = filter(f -> f != nothing, fields)
+    if length(fields) != 0
+        u = merge(fields...)
+    else
+        u = Dict()
     end
     return to_dataframe(u, abbreviation)
 end
diff --git a/src/postprocess_xdmf.jl b/src/postprocess_xdmf.jl
index c397524..3ad67ab 100644
--- a/src/postprocess_xdmf.jl
+++ b/src/postprocess_xdmf.jl
@@ -192,4 +192,3 @@ end
 function xdmf_save!(xdmf, filename)
     save_file(xdmf.xdoc, filename)
 end
-
diff --git a/src/solvers.jl b/src/solvers.jl
index 5fd06d7..ba4c4dc 100644
--- a/src/solvers.jl
+++ b/src/solvers.jl
@@ -9,7 +9,7 @@ type Solver{S<:AbstractSolver}
     problems :: Vector{Problem}
     norms :: Vector{Tuple}       # solution norms for convergence studies
     ndofs :: Int                 # number of degrees of freedom in problem
-    io :: Nullable{ModelIO}      # input/output handle
+    xdmf :: Nullable{Xdmf}       # input/output handle
     properties :: S
 end
 
@@ -457,15 +457,17 @@ function call(solver::Solver, field_name::AbstractString, time::Float64)
     return merge(fields...)
 end
 
-function get_temporal_collection(mio::ModelIO)
-    grid = find_element(mio.xdmf, "Grid")
-    if grid == nothing
+function get_temporal_collection(xdmf::Xdmf)
+    domain = find_element(xdmf.xml, "Domain")
+    grid = nothing
+    if domain == nothing
         info("Xdmf: creating new temporal collection")
-        domain = new_child(mio.xdmf, "Domain")
+        domain = new_child(xdmf.xml, "Domain")
         grid = new_child(domain, "Grid")
         set_attribute(grid, "CollectionType", "Temporal")
         set_attribute(grid, "GridType", "Collection")
     end
+    grid = find_element(domain, "Grid")
     return grid
 end
 
@@ -473,6 +475,7 @@ end
 function update!(solver::Solver, u::Vector, la::Vector; show_info=true)
     show_info && info("Updating problems ...")
     t0 = Base.time()
+
     for problem in solver.problems
         assembly = get_assembly(problem)
         elements = get_elements(problem)
@@ -483,27 +486,21 @@ function update!(solver::Solver, u::Vector, la::Vector; show_info=true)
     end
 
     # if io is attached to solver, update hdf / xml also
-    if !isnull(solver.io)
-        io = get(solver.io)
-        xdmf = io.xdmf
-        temporal_collection = get_temporal_collection(io)
+    if !isnull(solver.xdmf)
+        xdmf = get(solver.xdmf)
+        temporal_collection = get_temporal_collection(xdmf)
         frame = new_child(temporal_collection, "Grid")
-        time_item = new_child(frame, "Time")
-        set_attribute(time_item, "Value", solver.time)
+        new_child(frame, "Time", Dict("Value" => solver.time))
 
         # save geometry
         X = solver("geometry", solver.time)
         node_ids = sort(collect(keys(X)))
         geometry = hcat([X[nid] for nid in node_ids]...)
-        put!(io, "/Node IDs", node_ids)
-        path = "/Geometry"
-        put!(io, path, geometry)
-        dataitem = get_dataitem(io, path, geometry)
-
         ndim, nnodes = size(geometry)
         geom_type = ndim == 2 ? "XY" : "XYZ"
-        geom = new_child(frame, "Geometry")
-        set_attribute(geom, "Type", geom_type)
+        dataitem = new_dataitem(xdmf, "/Node IDs", node_ids)
+        geom = new_child(frame, "Geometry", Dict("Type" => geom_type))
+        dataitem = new_dataitem(xdmf, "/Geometry", geometry)
         add_child(geom, dataitem)
 
         # save topology
@@ -511,10 +508,21 @@ function update!(solver::Solver, u::Vector, la::Vector; show_info=true)
         nelements = length(all_elements)
         element_types = unique(map(get_element_type, all_elements))
 
-        element_mapping = Dict(
-            "Quad4" => "Quadrilateral",
+        xdmf_element_mapping = Dict(
             "Seg2" => "Polyline",
-            )
+            "Tri3" => "Triangle",
+            "Quad4" => "Quadrilateral",
+            "Tet4" => "Tetrahedron",
+            "Pyramid5" => "Pyramid",
+            "Wedge6" => "Wedge",
+            "Hex8" => "Hexahedron",
+            "Seg3" => "Edge_3",
+            "Tri6" => "Tri_6",
+            "Quad8" => "Quad_8",
+            "Tet10" => "Tet_10",
+            "Pyramid13" => "Pyramid_13",
+            "Wedge15" => "Wedge_15",
+            "Hex20" => "Hex_20")
 
         for element_type in element_types
             elements = filter_by_element_type(element_type, all_elements)
@@ -523,12 +531,10 @@ function update!(solver::Solver, u::Vector, la::Vector; show_info=true)
             element_conn = map(get_connectivity, elements)
             element_conn = transpose(hcat(element_conn...)) - 1
             element_code = split(string(element_type), ".")[end]
-            put!(io, "/Topology/$element_code/Element IDs", element_ids)
-            path = "/Topology/$element_code/Connectivity"
-            put!(io, path, element_conn)
-            dataitem = get_dataitem(io, path, element_conn)
+            dataitem = new_dataitem(xdmf, "/Topology/$element_code/Element IDs", element_ids)
+            dataitem = new_dataitem(xdmf, "/Topology/$element_code/Connectivity", element_conn)
             topology = new_child(frame, "Topology")
-            set_attribute(topology, "TopologyType", element_mapping[element_code])
+            set_attribute(topology, "TopologyType", xdmf_element_mapping[element_code])
             set_attribute(topology, "NumberOfElements", length(elements))
             add_child(topology, dataitem)
         end
@@ -551,14 +557,12 @@ function update!(solver::Solver, u::Vector, la::Vector; show_info=true)
         end
         U = hcat([U[nid] for nid in node_ids]...)
         unknown_field_name = ucfirst(unknown_field_name)
-        path = "/Results/$time/Nodal Fields/$unknown_field_name"
-        put!(io, path, U)
-        dataitem = get_dataitem(io, path, U)
+        dataitem = new_dataitem(xdmf, "/Results/$time/Nodal Fields/$unknown_field_name", U)
         attribute = new_child(frame, "Attribute")
         set_attribute(attribute, "Name", unknown_field_name)
         set_attribute(attribute, "Center", field_center)
         add_child(attribute, dataitem)
-        save!(io)
+        save!(xdmf)
     end
 
     t1 = round(Base.time()-t0, 2)
diff --git a/test/test_io.jl b/test/test_io.jl
index b3ce12e..077519d 100644
--- a/test/test_io.jl
+++ b/test/test_io.jl
@@ -3,18 +3,56 @@
 
 using JuliaFEM
 using JuliaFEM.Testing
-importall Base
+using LightXML
 
-@testset "create new result" begin
-    r = ModelIO()
-    expected = """<Xdmf xmlns:xi="http://www.w3.org/2001/XInclude" Version="2.1"/>"""
-    @test string(r.xdmf) == expected
+@testset "create new Xdmf object" begin
+    r = Xdmf()
+    expected = "<Xdmf xmlns:xi=\"http://www.w3.org/2001/XInclude\" Version=\"2.1\"/>"
+    @test string(r.xml) == expected
 end
 
-@testset "put and get result" begin
-    r = ModelIO()
-    put!(r, "/1/2/3", [1 2 3])
-    @test isapprox(get(r, "/1/2/3"), [1 2 3])
+@testset "put and get to Xdmf, low level" begin
+    io = Xdmf()
+    # h5
+    write(io.hdf, "/Xdmf/Domain/Geometry", [1 2 3])
+    @test isapprox(read(io.hdf, "/Xdmf/Domain/Geometry"), [1 2 3])
+    # xml
+    obj = new_child(io.xml, "Domain")
+    set_attribute(obj, "Name", "Test Domain")
+    obj2 = find_element(io.xml, "Domain")
+    @test attribute(obj2, "Name") == "Test Domain"
+end
+
+@testset "put and get to xdmf" begin
+    xdmf = Xdmf()
+    domain = new_child(xdmf, "Domain")
+    grid = new_child(domain, "Grid")
+    grid["CollectionType"] = "Temporal"
+    grid["GridType"] = "Collection"
+
+    frame1 = new_child(grid, "Grid")
+    new_child(frame1, "Time", "Value" => 0.0)
+    X1 = new_child(frame1, "Geometry", Dict("Type" => "XY"))
+
+    frame2 = new_child(grid, "Grid", "Name" => "Frame 2")
+    new_child(frame2, "Time", "Value" => 1.0)
+    X2 = new_child(frame2, "Geometry", "Type" => "XY")
+
+    add_child(grid, frame1)
+    add_child(grid, frame2)
+
+    dataitem = new_dataitem(xdmf, "/Domain/Grid/Grid/2/Geometry", [1.0, 2.0])
+    add_child(X2, dataitem)
+
+    println(xdmf.xml)
+    @test has_child(xdmf.xml, "Domain")
+    @test isa(get_child(xdmf.xml, "Domain"), XMLElement)
+    @test !has_attribute(xdmf.xml, "Domain")
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid/Time/Value"), 0.0)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[2]/Time/Value"), 1.0)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[end]/Time/Value"), 1.0)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[@Name=Frame 2]/Time/Value"), 1.0)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[2]/Geometry/DataItem"), [1.0, 2.0])
 end
 
 @testset "save results to disk" begin
@@ -26,7 +64,8 @@ end
     element = Element(Quad4, [1, 2, 3, 4])
     update!(element, "geometry", X)
     update!(element, "temperature thermal conductivity", 6.0)
-    update!(element, "temperature load", 12.0)
+    update!(element, "temperature load", 0.0 => 12.0)
+    update!(element, "temperature load", 1.0 => 18.0)
     problem = Problem(Heat, "one element heat problem", 1)
     problem.properties.formulation = "2D"
     push!(problem, element)
@@ -36,18 +75,43 @@ end
     bc = Problem(Dirichlet, "fixed", 1, "temperature")
     push!(bc, boundary_element)
     solver = Solver(Linear, problem, bc)
-    solver.io = ModelIO()
+    solver.xdmf = Xdmf()
+
+    solver.time = 0.0
     solver()
-    io = get(solver.io)
-    info("h5 file = $(io.name).h5")
-    E = get(io, "/Topology/Quad4/Element IDs")
-    C = get(io, "/Topology/Quad4/Connectivity")
-    N = get(io, "/Node IDs")
-    X = get(io, "/Geometry")
-    T = get(io, "/Results/Time 0.0/Nodal Fields/Temperature")
+    empty!(problem.assembly)
+    solver.time = 1.0
+    solver()
+
+    info(solver("temperature", 0.0))
+    info(solver("temperature", 1.0))
+    info(element("temperature load", [0.0, 0.0], 0.0))
+    info(element("temperature load", [0.0, 0.0], 1.0))
+
+    xdmf = get(solver.xdmf)
+    info("h5 file = $(h5file(xdmf))")
+    E = read(xdmf.hdf, "/Topology/Quad4/Element IDs")
+    C = read(xdmf.hdf, "/Topology/Quad4/Connectivity")
+    N = read(xdmf.hdf, "/Node IDs")
+    X = read(xdmf.hdf, "/Geometry")
+    T1 = read(xdmf.hdf, "/Results/Time 0.0/Nodal Fields/Temperature")
+    T2 = read(xdmf.hdf, "/Results/Time 1.0/Nodal Fields/Temperature")
     @test isapprox(E, [-1])
     @test isapprox(C, [0 1 2 3])
     @test isapprox(N, [1, 2, 3, 4])
-    @test isapprox(X, [0.0 0.0; 1.0 0.0; 1.0 1.0; 0.0 1.0]')
-    @test isapprox(T, [0.0 0.0 1.0 1.0])
+    X_expected = [0.0 0.0; 1.0 0.0; 1.0 1.0; 0.0 1.0]'
+    T1_expected = [0.0 0.0 1.0 1.0]
+    T2_expected = [0.0 0.0 0.5 0.5]
+    @test isapprox(X, X_expected)
+    @test isapprox(T1, T1_expected)
+    @test isapprox(T2, T2_expected)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid/Time/Value"), 0.0)
+    @test read(xdmf, "/Domain/Grid/Grid/Geometry/Type") == "XY"
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid/Geometry/DataItem"), X_expected)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid/Topology/DataItem"), [0 1 2 3])
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid/Topology[@TopologyType=Polyline]/DataItem"), [0 1])
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[1]/Attribute[@Name=Temperature]/DataItem"), T1_expected)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[2]/Attribute[@Name=Temperature]/DataItem"), T2_expected)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[end]/Time/Value"), 1.0)
+    @test isapprox(read(xdmf, "/Domain/Grid/Grid[end]/Topology/DataItem"), [0 1 2 3])
 end